From personal experience, that of playing a dedicated Wizard to 8th level in a 3.5 game, I have to say that the expense of gaining more than the free '2 per level' SUCKS. It's seriously unreasonable and basically screws the Wizard class.
Sure, you can copy scrolls. But that assumes that your GM is accomodating in providing exactly the spells that you want at that moment. If not, then add the cost of the scroll to the cost of writing the spell into your book and it quickly becomes prohibitive.
1st = 25gp scroll + 100gp scribe = 125gp
2nd = 150gp scroll + 200gp scribe = 350gp
3rd = 375gp scroll + 300gp scribe = 675gp
4th = 700gp scroll + 400gp scribe = 1,100gp
...and so on. Probably less of a bother at higher levels, but at 3rd-6th level, you're definitely screwing your wealth by taking this tack. OTOH, if you don't, then you miss out on a lot of very good 2nd and 3rd level spells. Meanwhile, your Cleric buddy has a list of spells longer than your arm that he can sling around virtually at will.
Downtime is another issue, but YES, it makes a serious difference. Unfortunately, all too many GMs (in my experience again) are into the whole concept of the fixed length "stop the evil guy before X date" plot concept, because they think it heightens the tension. I believe that such plots should be limited in scope to one adventure or not more than about three levels maximum, with long breaks between them.
Bottom line, if your GM doesn't make a special effort to accomodate your spell acquisition as a Wizard and give you reasonable downtime, then you're probably better off playing a Sorcerer, because you'll only have slightly fewer spells available but can cast them more often. You also don't have to deal with the whole Spell Book problem.