I started bike commuting on most days about 2.5 years ago on a used Trek 4500 (2002 model I think). For 2 years, I had a flat 1.5 mile commute each way in SoCal. This summer I moved to the Seattle area (Eastside) and now have an 8 mile commute with several steep hills (both downhill and uphill). I'm currently commuting 2 miles to the bus in the morning and 8 miles back in the evening on roads (sometimes rough), but plan to do round trips eventually. I've also been riding more on the weekends lately, up to 30 miles per day.

I switched the Trek to road tires and recently completed $250 of maintenance on it. But I don't know how it was treated before I bought it and something else could always break. It's been good to me so far, but there are a couple of things I'm not happy about:

1. Climbing hills is painful. I've read that replacing the suspension fork with a rigid fork would help, though I'm not sure how much. The stock fork has no lock out.
2. I'm often in the highest gear, so a road chainset is something I'd like to get.
3. I haven't had too many problems with the brakes yet, but I ride in all weather and disc brakes are probably a good idea. This is lower priority for me though.
4. I definitely feel that a lighter bike would make 20-30 mile weekend rides more enjoyable.

I'm trying to decide what to do, and hope to receive some advice from all of you. I think I have two options here:

1. Buy a new bike for commuting and pleasure rides that can handle roads and is not too expensive so I don't mind riding in the rain on it, putting it on the bus, etc... and keep the Trek as a backup in case that one fails.
2. Upgrade the Trek with a new fork and chainset, and buy a road-like (maybe touring) bike for longer rides and two way commutes in good weather.

Any thoughts on which way I should go? Is it worth investing more money into an older mtb? I also don't know if I'd be more comfortable on a different type of bike - I have very little experience except on this bike.

Thanks in advance!