Perfection not required; or, the joy of editing
It is very nice when someone adds a complete, well-written, original final draft of an article to Wikipedia. This should never be discouraged.
However, one great advantage of the Wiki system is that incomplete, poorly written first drafts of articles can evolve into polished, presentable masterpieces through the process of collaborative editing. If this does give our system an advantage over other systems of producing similar end-products, then it would be very wise and desirable to encourage this process as much as possible.
One person can start an article off with an overview or a few random facts. Someone else can add the opinion of some small minority. The next person can round off the article with additional opinions. Someone else can play up an angle that has been neglected. The next person might have a list of facts and figures to include.
As all this material is added, anyone can jump in and refactor to turn it into a more cohesive whole. Then more stuff will be added, then more refactoring, and the article will spiral ever-closer to the perfect final draft.
During this process, the article might look like a first draft, or worse, a random collection of notes and factoids. Rather than being horrified by this ugliness, we should rejoice in its potential, and have faith that the editing process will turn it into beautiful prose.
On editing styles
Generally, different people here have different editing "styles." Some people do rather little editing, and focus on contributing new content. Some prefer to improve and greatly expand old "stubs" and articles. Some like to make relatively small copyediting and page naming changes. There's room for all of this on Wikipedia.
There are also different editing styles in the sense of how bold people are willing to be. Generally, most of us think we should be bold in updating pages. Virtually no one behaves as though previous authors need to be consulted before making changes; if we thought that, we'd make rather little progress. Quite to the contrary, some of us think one should not beat around the bush at all--simply change a page immediately, when one sees something perceived to be a problem, rather than to discuss changes that need to be made. Discussion, on this view, is a last resort. Then there is a more intermediate view, according to which dialogue qua dialogue should be respected, but at the same time a minor tweak early on can avoid a flame war. On this view, to edit radically or not will often depend on the context--which seems reasonable enough. Again, there is a place for all of these attitudes on Wikipedia.
With large deletions or replacements, it might be better to suggest changes in a discussion, lest the original author get discouraged and quit posting. One person's improvement is another's desecration, and nobody likes to see their work just flushed without warning. Then again, oversensitivity can be detrimental to progress, and they could just restore it.
So, whatever you do, preserve information. If, in your considered judgment, a page simply needs to be rewritten or changed substantially, go ahead and do that. But preserve any old contents you think might have some discussion value on a /Talk page, along with a comment about why you made the change. Even if you delete something that's just plain wrong, odds are that it got there because someone believed it was true, so preserve a comment that it is in fact wrong to deter later editors.
In any event, whether you decide to edit very boldly or to make /Talk page inquiries first, please bear in mind that Wikipedia is not a discussion forum (among the other things it is not). Wikipedia is a very energetic place, and it's best for the project as a whole if we concentrate our energies on improving articles, rather than defending our pet theories, ideologies, religious, etc. Some consideration of Wikipetiquette wouldn't hurt.
So much for editing articles; now about editing talk pages.
Editing and refactoring /Talk pages
A talk page is created by writing /Talk at the bottom of a page; this creates a subpage. Inevitably, there will arise situations in which collaborators on an article can benefit mutually from discussing the article--thus we have started the convention of using talk pages.
Editing a talk page is rather easier than editing an encyclopedia article page, because all one is required to do is tack on one's opinion. This, however, can very often prove to be a distraction from the harder but more rewarding work of actually writing an article. Often, for some people, it can seem more interesting to engage in verbal fisticuffs than actually work on encyclopedia articles. The wiki software permits this--but that doesn't mean it's a good idea. It's probably not a good idea if the discussion in no way contributes to the article's improvement. It's only the habits we encourage that keeps Wikipedia from turning into another H2G2 or Everything2. We really don't want Wikipedia to go that route. Please see Wikipetiquette for some suggestions on how you can avoid overusing talk pages in this way.
A point of terminology: the notion of refactoring, in the context of a wiki, means basically the rewriting of a page so as to preserve all the useful information on the page. It's relatively rare that one needs to entirely refactor a Wikipedia article--usually, edits and additions are what is necessary.
The purpose of talk pages is to assist in creating better articles. Therefore, the purpose of refactoring talk page discussions is to help create good encyclopedia articles, at least in the long run. A short-run purpose is to channel a discussion in a useful direction, i.e. to help aim it at the future time when it can be used in an encyclopedia article.
Regardless, there are a number of talk or other discussion oriented pages which could use a bit of traditional Wiki refactoring. There's useful content there, sometimes, that can be transferred to the article itself. Sometimes large chunks of old talk pages can be completely wiped out with no harm done--feel free to do so, unless you think there's some value in preserving the discussion. In refactoring a talk page, one solid recommendation is to use the traditional wiki refactoring technique of adding a summary with whatever consensus we've arrived at the top, grouping separate discussion items together, and placing them towards the bottom.
See also Wikipedia policy.