tl;dr: What bad things will happen if I do a factory reset?
So I've had this original Droid for about a year and a half. I love this phone, and if only I could get it to be a bit faster and have a little more internal memory I'd keep it forever. However, it had been around for quite a while before I jumped on the Android bandwagon and it's getting pretty creaky in the joints. Further, my contract isn't up until next April.
Over that time I have installed and uninstalled a lot of applications (often to answer questions here or, more likely, from recommendations here). I have tried no fewer than five different home screen launcher apps.
I have streamlined the apps I'm using and moved everything possible to the SD card. Still, performance just isn't that good. I don't want to root (although I've considered it), but I need this thing to carry me for eight more months.
Could a factory reset possibly help? What is the downside to doing a factory reset?
I'm not concerned with losing anything important. Between the Market and AppBrain I have no fear that I won't be able to get key apps back. I also have all of my important data syncing to the cloud so I've no worries there.
Is there anything lost that I can't recover myself? For instance, am I going to have to go back to the Verizon store and have them reprogram my phone number? Is there any reason I shouldn't just go ahead and to the reset?
Update: So I took the plunge yesterday and everything worked out fine. I use Google 2-factor authentication, and that complicated things a little bit. Once I got past that it has been fine. I have quickly the discovered the apps I really need, and have been enjoying much "snappier" performance.
I'm just sorry that I can't accept multiple answers. These have all been very helpful.