I have an old Trek 800 mountain bike that I use as a general purpose bike. It's about 14 years old with a 6-speed freewheel. I noticed this winter that the hubs were getting wobbly. I tried tightening them up but in order to get rid of the wobble, I had to tighten it so much the axle would rub against the bearings creating a lot of friction.
I took the plunge recently and bought a new wheelset from my LBS. He had some great deals on Bontrager wheel sets. I also bought a new 8-speed SRAM casette and some new shifters. I installed these components on last week and tuned the bike up and I'm really happy with the results. I was surprised at how much of a difference brand new, good-quality wheels and hubs makes! I seem to coast forever when compared to my old wheels. Also, my old 6-speed freewheel had a 34 tooth mega granny gear to help when I'm hauling kids or groceries up the hills here in New Hampshire. However, the new 8-speed freewheel, while it only has a max 32 tooth gear, has two more cogs in the back and shifts a lot more smoothly. Plus, it provides me with a greater range of usable gears to choose from.
I find that with the new 8-speed cassette I can pick a more efficient rear cog to use and get up hills faster while still doing so very comfortably.
Anyway, I wish I had invested in these upgrades a long time ago! This thing is a joy to ride.
Now only the front derailleur, the brake levers, the seat post, the frame, the handlebars and headset are original. I think I've upgraded everything else over the past couple of years. What an awesome bike.