Why not pursue a dream? I think this line says it best: "Debt kills small breweries." http://www.soundbrew.com/projectnotes.html
If I had an extra $500,000 just sitting around, I'd be more than happy to pursue the dream. That is sort of the problem with this industry... You can't just open a storefront and start making and selling small widgets. There is significant capital required to acquire property, purchase a brewhouse, a mind bending amount of red-tape (although with the explosion of craft brewing, most state agencies are really good about getting you pointed in the correct direction and walking you through the process - unlike say 10-15 years ago when the people working there didn't know the process either), and you will be operating at a loss until you can build a distribution channel. So, if you were leveraged with $450,000 of debt at 8% on a 10 year commercial business loan, you're looking at something like over $5400 in debt service each month. If you are serious about doing this, you have to ask yourself, how long can you sustain that and draw a salary for yourself until you start turning a profit?
So on a 15 bbl system, you're brewing about 35 kegs at a time. Assuming you can sell those out regularly, you have a new problem: your choke point - how many fermentation vessels do you have and how long your beer is going to sit in them. Should you have spent the money for a 30bbl system initially instead - instead of going through the whole capital improvement process again to upgrade your brewhouse.
Anyways... I might be rambling a bit - but you get the idea... lots of things to think about and a lot of risk.