What COULD the future hold? Well, you COULD have several All-stars there, with a couple of #2 type starters. That said, you COULD end up with a bunch of fringe players as well.
If you're choosing whether to keep a prospect or play for this season, play for this season. No rookie is a sure thing, and even top players don't necessarilly come out of the gate the first time they taste the majors. Just look at the 4 players you listed. Only Pujols did well the moment he hit the majors. Beltran had a cup of coffee prior to his first full year, but Vlad and ARod each had part time for two years before their first big (and complete) full season.
So, using Marte as an example (as I'd consider him the best of your prospects), even if he were the next great thing, the odds are he'll be of little help this year even if he comes up, and 2006 is no sure thing.
The rest of your prospects, which include many good ones and a couple I have, all have some level of risk. Barfield has 21 K in 63 AB at AAA. Gathright seems trapped and seems to not have the blessing of the Rays. I like Hinckley, but he very well could be a #3 starter. Hamels has talent, but maturity issues and will be in A ball. I also like McGowen.
But, as a whole, and outside of Marte, I would not be afraid of trading any of them for help this year as I doubt any of them (outside of Marte) will be much help until 2007.