BMX - 20" bmx: Trade in or upgrade? Advice please.

I am a college student who goes to school on a small, flat campus. A bike is not necessary for me to get to where I need to go, but it is useful, and I enjoy riding. I currently have a 2004 Specialized III black, 20" bmx bike, and I have been having minor troubles with the bike since this summer when I realized the thrill of trail riding.
All june I had been driving from my house to relatively close trails, and riding very bumpy trails so that I could do small jumps. This caused immense stress on the crankset (Specialized tubular Cr-Mo 3-piece, L & R drive compatible, 180mm) and at the beginning of july, I noticed that the heli-coils holding the pedals to the crank arms were becoming stripped. Aftrer taking my bike out on a long trail one day, and having a pedal fall off a mile out, I decided to take the bike in to the shop I had purchased it from. I left it with them for 3 weeks, and then they called me one day to let me know they couldn't get the parts. instead they replaced the crank arms, but no other parts of the crankset, with crank arms from a FSA Nasty Boy 3-piece crankset. I need to have the middle piece replaced, as there is residue from rust on it, and there is already oxidation on the crank arms.
Another problem I am having is with the brakes. they simply don't slow me down, let alone stop on a dime. I tried tightening the brake line, a few weeks ago, and ended up with tighter brakes, but a semi-frayed brake line. I think I may just need to get new pads, a new brake line and brake set could be in order however.
As I stated before, I enjoy riding on trails, and the street tires on the Fuse, don't hold much traction on the loose soil of the trails I enjoy riding on. I currently have a flat tube, and will need to take the tire off anyways, I've been considering putting on tires with trail traction, and am wondering if that would be a good idea or not.
I also have a rusty chain. I need to get a chain that stays taught and is rust resistant, if that is a possibility.
So, the question comes down to whether on not I'd aught to buy the parts and fix the bike myself, take it in to a shop, or simply trade the bike in and get a new bike. the work that I had done on the bike this summer cost $110, and the bike initially only cost $450. I would like to be able to fix the bike up, as I love its feel, and the weight, but I am open to suggestions.

thank you for your time and help


advice on tires
advice on brakes
advice on crank

Tires you can look up maxxis or tioga

brakes sounds to me you would benefit from a new brake cable and pads

so danscomp.com

and crank as well you can find that at danscomp.com also.

The crank there is so many brands out there. I prefer Profile, some odyssey, etc so i am not going to push a brand on you.

As for a chain. Sorry to say but there isn't a rust resistant cahin out there. Just proper maintenance with Finish line Chain lube.

Finish line dry FTW on the chain lube. The bike is solid, no need to trade it in. For tires there's alot of options, if you want to protect your rims and avoid flats look at something with a high PSI rating ex: 80 - 110 psi, and be sure to keep them pumped rock hard. At least 75 - 80 psi. This will protect your rims from case dents flat spots and keep the wheel true longer, it will also prevent flats more effectively and allow the bike to roll faster smoother and coast longer with less effort while pedaling. Id look into Fly rueben tires, odyssey path, dirt path, and aitken tires, fit FAF, and duo is out with a nice looking dirt tire now too. All these tires will be fine for riding the streets hitting up a skatepark here and there and will own at the trails. A comp III or a holy roller on the front would be alright as well, but keep in mind the psi ratings. As for the brakes, the first thing i would do would be replace the cable and clean the rim and pads very well. Take the pads off and sand them or rub them on a side walk or street untill they are clean, this will help significantly. As far as dialing in the brakes there are lots of little techniques but your best bet is to take the bike to a shop have have them tune the brake. The cranks sound fine, the "middle piece" (spindle) is probably fine, just take the crank set apart and thoroughly clean everything, then rebuild with ALOT or grease. I stress the grease, use more then you think you need and wipe the excess away after assembly.