"Disguised synonyms" themes work best when the synonyms are . . . well, well-disguised.
That's why they pay me the big bucks, people.
SEATTLE SLEW is a perfect way to obfuscate the "a lot" meaning of SLEW. Horse owners and the weird names they give! PAPAL MASS also works, since the religious sense of "mass" is different from the "large group of things" sense.
BATTERY PACK, not so much, as that means "a lot of batteries put together." Better would have been something like VACUUM PACK.
HEAP is a tougher one, as there is no other meaning of HEAP than "a big pile." What would have been another word to work with, less directly? How about CARBO LOAD?
To have or not have a revealer, that is usually the question. Not today, though, since newer solvers would almost definitely miss the theme concept without it. Heck, some experienced ones, too! I liked IT MEANS A LOT TO ME, although simply IT MEANS A LOT feels much stronger. Less is more.
IT MEANS A LOT could have been placed into the last themer position, too, delaying the a-ha moment until the end of the solve. It's not as fun when you hit the revealer halfway through the puzzle, making the rest of the solve a bit of a let-down.
I loved the long bonuses, and if you're going to include six of them, Gary laid them out perfectly. Staggering WORRISOME, THE NATURAL, OPEN ARMS, LEGAL PAD, GULF STATES, MOTOR RACE up down up down up down, spread across the columns, is the best way to create spacing, working around those five themers.
Whether you should or not is a different question. See: ALCAN, AGITA, OTT crossing STENS for Pete's sake that's just taunting newbs! See also: GESSO crossing SKOL. As much as I appreciated those six long bonuses, limiting them to four would have made for a much more appealing puzzle.
Overall, a strong theme concept, but the puzzle could have used both theme and grid revisions.