Depends how happy you are with the setup and why you'd be upgrading.
For example I'm still sat on a 2.2GHz Core 2 Duo with a Geforce 8600M GT laptop, although I do have 4GB of RAM in it, but the only real reason I have to upgrade is to speed Windows 7 up (I dunno WTF they've released in the updates over the last 3-4 months, but the start-up and login speed have shot to Win98-on-a-486 levels, even on a clean install with nothing but updates). I've not come across any game recently that I feel is worth the money and wouldn't run on this setup.
So, yeah, if the machine is working for you, then stick with it. More RAM can never hurt though... Especially if you use Chrome.
Don't know what you've done, but my Win7x64 still boots amazingly fast for me. Beats a fresh XP from POST to login, and from login to desktop. I also have loads installed.
@dschallert
The usual upgrate ram to speed a machine up, isn't a certain fix all. If you're not using the 2GB then adding more won't do anything noticeable. If you get process explorer, and open the sys info window (ctrl-i), you'll see a graph of past RAM usage, which can help identify if you're using lots or not. If the pagefile is being used loads, then that can show the system would benifit from more RAM. Though it depends on what you are doing.
Running XP right? Win7 is generally more responsive than XP, at least this is what I've found, having upgraded 3 XP machines to win7 without hardware changes.