Red, most of the things you mentioned there will simply free up hard disk space on the server, although shifting stuff to members only is a good idea.
If you really want speed - you need to upgrade hardware. What sort of processor do you have at the moment? How large and how fast is your harddrive? 1GB of memory - is is SDR or DDR? Consider getting a couple of new drives and connecting them via RAID. This will often speed up disk access times by 33%. Faster processors - in the 2.5gHz-3gHz range with 1GB of DDR memory and a 100GB RAID drive will easily handle 1,000,000 hits a day.
As for security - under vBulletin IP banning is already possible. Also, I wasn't aware that normal users can view other users IP addresses... mods can view them all, naturally. The only problem with IP banning is that some users are still on dial-up, so all they have to do is reconnect, get assigned a new IP, and re-register. Banning an entire subnet is just not acceptable.
One more thing - make sure you've shut down any non-essential services on the server. What OS are you using? Windows? If it's Windows, you should be using NT/2K or even .NET Server. If it's none of those, consider switching to Linux - it's a free download, or less than $100 a copy off the shelf. It is known to be more stable and more reliable, and excellent for webservers.