Having been the pilot on hundreds of pax/cargo mission in US and OUTCONUS, as well as having having hopped a few places myself, my opinion is that Space-A is essentially worthless. Unless you're traveling on a route that has scheduled missions, with relatively large aircraft, and the schedule fits into your plans, you stand a real chance of sleeping in a terminal somewhere and eating out of a vending machine.
Space-A is great if you don't care where you're going or when, or if you have to sleep on the floor of the pax terminal and not shower for a couple of days. We would see the same retirees over and over again with their crap stuffed in a suitcase, begging for rides from the terminal to a hotel because they couldn't catch a hop for a day or two. Fine for them, they have no where to be! Any number of things will cause a well-planned trip to go bad including weather, mechanical problems, re-routes by JOSAC, etc.
The best way to do it is if you know the crew and they are going somewhere for a specific amount of time, like a det or a 3 or 4-day round robin, and then coming back. Obviously this takes some inside gouge that's not easy to get as an HPSP student on summer break.
My advice if you want to run off to someplace at the last minute is get one of those internet deals, at least then you have a return ticket.
Sorry to bust your bubble, but the fact is, aside from the schedule routes, most of which are either MEDEVAC or OUTCONUS Cat-B's, Space-A ain't all it's cracked up to be.
Spang