If your boot up time is unchanged, all you can do is clean up the drive. I use the windows clean disk program, and a free program called "ie privacy keeper". You can also test the drive performance using the manufacturer's software. The windows experience meter always has at least one device dropping the average. Don't worry about it too much.
10k rpm does not directly translate into a high data transfer rate. Newer high density 7200 rpm 1tb drives can transfer faster. Still with fast access, the VR is still about as good as it gets until you go with a good SSD
5.9 is the maximum score for a disk under Windows Vista.
In Windows 7, they extended the score to 7.9 to accomodate SSDs, which are way faster then mechanical disks. Since you have a mechanical disk, you're still stuck at 5.9.
BTW the "Windows Experience Index" is a very coarse guideline, not a benchmark. It's not a good tool to use for performance testing.
You can get up to around 6.5 with hard drives, though it is hard (the 6.5 that I saw was with a couple 15k drives on a hardware RAID controller with a ton of cache). To get up into the 7+ range though, you do need an SSD. The score isn't just disk transfer rate - it accounts for access time as well, and SSDs are unmatched in that area.
The main drawback is cost per gigabyte. Read the current reviews, and do not read too much into synthetic benchmarks. Today, I think the intel X25-M are the best drives without write problems. Kingston has a 40gb drive for the OS for about $130. The key is how big a buffer the drive has, and how well it handles small writes. If you will use windows-7, you want a drive with TRIM support.