Yes, many DIY designs are excellent. Remember that commercial amps charge for labor, overhead and profit (and justifiably so), so a similar amount spent on DIY gets you the finest parts and possibly into a much more expensive amp than you can afford.
Another huge benefit is that DIY amps are picked over publicly by very knowledgeable people who often build them. If there is a problem in the design or a small tweak that improves it, those usually get added to the design. Commercial amps rarely get this kind of scrutiny. Though many designers are smart and talented, nothing irons out the final details like making your design public.
Another reason is that DIY designs often use more unconventional designs than commercial amps. They're designed for fun and to learn, not necessarily to develop a produc line. So if you like things a little out of the ordinary, DIY will give that to you.
Finally, being able to pick your own parts and incorporate neat extras is wonderful. A couple weeks ago, I picked up a bag of nifty tie points. These things are nickel plated solid copper. I've looked and can't find these on the market. But $10 got me enough to use in several projects. These are going to make for nice amps - the layout will be clean and I'll set it up so it'll be a snap to take measurements and (eventually) replace stuff that wears out.
So go ahead and build an amp. The only risk is that you'll get hooked and end up with too many projects.