Parelli is good, if you want to dedicate the time. I have gone up to level 2 with my horse... I think Parelli is very, very good for ground work and teaching the person... but I do not think parelli is all that realistic if you want to show your horse, riding-wise. If you want to go to a few local shows and stuff its fine, but I don't think it makes your horse reliable.
I remember I went to one of the clinics and linda parelli's horse refused a jump for no reason, one that he'd done before. This isn't some huge, horrible problem, it's just that in today's show world horses have to be consistent and reliable... I think their horses are willing and love what they do, but I don't think they can attain the same high level as some other trainers can, without parelli.
With that being said, if you do want to do a lot of showing... I wouldn't advise getting the tapes and trying to do them now. There's a pretty long 'no riding' in the beginning of level one... and I know that when you're showing, you usually don't have a lot of time to let your horse not be ridden! I would tell you to get them later, during the off season, and only go up to level 2 (3 if you want to shell out the money).
Also, the parelli equipment is worth EVERY penny. I know they're expensive, but they are better then every rope halter/hackamore I've seen. The bridle's are a waste of money because they're no different then a good quality one at your tack store, but the halters and ropes are fantastic. I use them on all of my horses.
Just remember that there is a lot of marketing in parelli to get you to buy their things... I love the program, just not the needless advertising. There are some things you need... and some you don't.