RAM can help with the "zip" you're talking about, but it isn't the only thing that affects performance in OSX. On your particular system, no matter what you do OSX is going to feel a little slower than OS9 because it is simply a beefier OS and the eye-candy takes longer to render onscreen than the visuals in OS9. Actual application-level tasks will run as fast as anything, but the "snap" to the interface isn't quite there.
That said, a couple things that can help: Make sure you have a good chunk of free space on your startup hard drive; at 5-10GB is generally recommended. Restarting once a week or two generally helps as well, but then it sounds like you've restarted recently. If you don't have your Mac awake during the night running the periodic tasks manually can help a bit; there are applications like Panther/Tiger Cache Cleaner that will do it for you, or you can use the command line: Type "sudo periodic daily", "sudo periodic weekly" (this one can take a while), and "sudo periodic monthly". You can also use PCC/TCC to clean out other caches, which can sometimes help.
Finally, on lower-end machines like yours, you can use TinkerTool to tweak the interface a bit and turn eye-candy off: shadows, zoomy-effects, etc. This can make a noticable difference, depending on what it is about the lack of "zip" that's bothering you.
If all of the above fail, your computer just isn't fast enough for your taste or there's something wrong with your installation; reinstalling the most recent "combo" updater or reinstalling the OS from scratch (full reinstall, not just an upgrade) might be the only solution.
Funny, though; 10.3.9 seems to run reasonably smoothly on an eMac 800 with 512MB of RAM, so unless you're sensitive to slowness in the UI perhaps there is something "wrong" with your system.
On a related note, not to be insulting, but assuming that OSX's virtual memory system is why it feels slower than OS9 is patently ridiculous--you might try reading up a bit on how memory management works before assuming things like that.
Were OSX to have a primitive memory management system like OS9 it MIGHT be a hair--emphasis on a hair--faster in situations where there was lots of RAM to spare. It would also usually crash systemwide when an application died, would be far slower re-starting applications or re-accessing previously used data, would waste monumental amounts of RAM when you had apps like Photoshop open without any documents, and would still be every much as much a pain to manage as it used to be. The ability to launch, say, Photoshop and have it take as much RAM as it needs at a particular moment--be it 100MB or 2GB--is more than a little handy.