install shouldn't effect on your phone's speed. it's the ones that are running in background that will make it crawl. some apps aren't written as well as others, and that'll create problems. task killing will help in some scenarios.
That sounds nice but the truth is apps running in the background and task killers are not the answer. What's probably going on is you have one or two apps that are slowing it down. Droid is very good at running it's own memory.
My suggestion is when you see it start to bog down give it a restart. I usually do mine once every other day. If you have any virus protection remove it, as well as task killers. Both are resource hogs, and task killers are fighting the Droids own memory management system.
Also get something to clean the cache of your apps. I use Cache-mate for rooted users, if you're not rooted then find something else, just search for cache cleaner.
Hope this helps.
See if that doesn't help you out some. Sometimes it's the simple