it all depends on what you want to do. If you want to try and make a living off of recording and find a job in the business somewhere, any amount of learning whether it be at a school or on your own can't hurt. So I don't think schools will be a "waste of money." Experience is experience...and you can get some of the experience in a classroom or studio working with teachers who have done this stuff before.
So many people in this industry are quick to judge schools and their teaching of students...but they forget that a lot of the teachers in these schools have been recording for years and have a lot to teach. Not to mention a lot of these schools have great facilities with awesome gear. So combining a teacher with years of experience and the equipment to learn on....I don't really see a downside to that. It'd be similar to walking into a studio and interning or assisting right away.
As far as just taking the $20K and putting it towards gear...that'd be awesome, if you have 20K sitting around. Most people don't. And the 20K you're going to get for school you usually get from a bank. It's going to be hard to get a bank to give you 20K for just buying gear. Not to mention, the 20K won't get you a 96 channel SSL to learn on.
You get out what you put in. If you work your ass off and try and get as much hands on time as possible, you'll learn a lot. You learn from someone else's experience. You learn proper micing techniques that have been used for years, studio ettiquete, the business side of things, how to work with analog tape, patchbay work, electronics, using MIDI, different software programs...some teachers may even go as far as to show you what they would do with a mix or when recording a certain instrument.
Look at your local Junior Colleges if you can't afford schools like Full Sail. Those are usually the cheapest places to go for short term. Some studios in your town may even offer classes...I know one here does.
If you perform a critical analysis of Full Sail's public job placements vs. the number of students you will see that, despite the marketing bullshit, they are only placing a small percentage of students.
This is maybe true for the people who did terrible at Full Sail...but there are idiots at every school. I for one got a job right out of school and everyone I still talk with has jobs as well in studios. Again, you get what you put into it. Full Sail can help you with placement, but they don't get the job for you. It's up to how well you interview as well as a little bit of luck (as with every job).
Some people also don't learn well on their own. Take a look at this forum here. How many 16-18 year olds get their parents to buy them everything under the sun to start recording and they jump on here the first night they get everything and post "I'm confused, can someone explain to me how to hook up everything and record?"
Not to mention in some school settings this stuff is forced into you 5-6 days a week, 9 hours a day. You get much more hands on experience and studying of this stuff than an average hobbyist does on the weekends when he's not at work. You start acting like it's a full time job right off the bat and soon it's all you know.
Then there's the most important part of the recording schools...networking! You'll meet lots of people and want to maintain those relationships down the road because you never know if it may mean a job one day for you.
Just my $.02