goodness, just woke up from a cat nap, so I'm still kinda bleary-brained....
One of the things that I just love about you, Melissa (and Jas and Rachel and others) is that you all have a brain. Seriously, it's wonderful (and sexy)!
It's a fair question, 30 minutes, but I must agree: in a perfect world, yes to the 30 minute sessions.
Alas, our world is far from perfect. So many nut-jobs, stalkers, and doh-doh birds. For myself, if I had a 30 minute session, I can't imagine having it all in such a brief amount of time. For me, that's just not possible. But, for oral fun only, I think it is. Ah, but then there are the whack-o's that want to feel like they're in control for those 30 minutes of their life . . .
Yes, absolutely, to what Jas said: Safety, Fun, and Profit.
Living where I live (Arkansas), I don't have the opportunity for a quickie, so I don't shop at the Five-and-Dime. My days and nights are spent mostly window shopping, which is fine for my budget 
So, I would be looking for longer sessions, maybe even dinner, planned in advance, creating a connection, that kind of thing.
This is where legalization of the hobby would help because one could advertise and screen clients without fear of LE.
I'd say, keep the 30-minute in your back pocket for great guys like the Dog, but I wouldn't be so quick to extend the offer to an unknown. Seems like it would be high risk with little pay-off.