In my opinion, the best route to go is... save up your loot and do several upgrades at once to get the benefits each aspect has to offer. No one single thing you can bolt on is going to net huge results... but combine a couple at once, and you'll see some benefits. The big gain upgrade points would be: compression, carb, cam, exhaust port work/cylinder head work... combined together, as each on it's own really does not add up to being worth the expense of each on it's own.
Honestly, the best thing you can do now, is make sure everything is tuned up correctly... make sure your ignition is at least half way decent (if it's points, ditch them for at least a petronix, or as much as a ready to run MSD) as ignition will create more problems if it's crappy than just low hp (misses, won't rev, hard starts, etc...)... and make sure your pump is in decent shape. Often times... a well tuned stock engine and pump will run day and night better than a so-so engine and pump with a bunch of bolt-on's thrown at it. And as long as it runs fairly well, and runseach time you want to use it... you can stash away loot to do a big upgrade that will net some real gains.
