The marina owner is right about the ablative paint, it should be fine..most northeast boats sit six months out of the water, and the ablative paint is fine to go back in, no worse for no wear. The patch colored blue sounds like the hard bottom paint, if it were barrier coat it'd be grey or black.
If the ablative paint has stuck satisfactorily, and you don't have blisters, don't wate your money doing a bottom blast, you'll end up spending several thousand dollars and lots of work time to get back to where you arleady are. Just have the bare spots sanded well, then put a few coats of paint on those areas. You don't paint an ablative bottom unless it needs more paint due to the sloghing off in the water. Simply put a coat on every year and you are likely to end up with a thick paint layer, which will flake, and then you HAVE to blast the bottom and start over.
As to the bare spots, they will be fine other than they may grow nasty marine stuff like barnacles. If you can get a diver to scrub those areas periodically you may be able to contain nasty growth, otherwise get a good sander from Santa.
Certified...in several regards...