Newbie Trying To Upgrade Bike Components
I have a problem. I know nothing about bike mechanics or how to upgrade. I don't know gear ratios or whatnot. I have had a Trek Navigator 300 Comfort/Mountain bike for at least 4 years. The past few years I have been hitting the local (paved) trails hard. I can get up to around 20-22 MPH easy in the highest gear on downhills, but I average about 15.5 MPH.
Shifters SRAM MRX Pro, 8 speed
Front Derailleur Shimano C102
Rear Derailleur SRAM X-7
Crank Bontrager Sport 48/38/28 w/chainguard
Cassette SRAM PG830 11-32, 8 speed
Pedals Dual density platform
Tires 26"x1.95" Comfort/Mountain
I am thinking about trying to turn this into a commuter bike. Does anyone have any ideas short of getting a road bike for making my ride faster and more efficient? It is a great bike but I need something that's faster and easier on my knees (rather than riding in top gear all the time).
I have gotten a suggestion on getting slicks for my rims. Does this add speed? My qualm is if the gear ratio is bad to begin with, it won't help, right?
Do I need new handlebars or something? A new crankset? My crankset is kind of cracked anyhow from use and abuse. If I replace the crankset with new gear ratios, do I need to get a new cassette?
Also, what about clipless pedals? Any suggestions? My feet have never felt right on the pedals I have....
Is it even worth the hassle trying to upgrade my bike?
Thanks for any help or suggestions!