I'm admittedly playing messenger here - since I haven't myself, but talked with a few friends who are in that exact category.
The general idea I've heard is - go in apples to oranges if you want the best mindset.
MNSSHP was more of an "event". It had more unique offerings, and the rides were secondary. While not nearly as much and a TOTALLY different audience, its best comparison would be Halloween Horror Nights. Where the focus is really on the shows, candy, wearing costumes, special food, overlays, etc. - and having short lines was just an added perk should you want to take advantage to that.
Boo Bash is an after hours event. So, that means the short lines are really the focus - in an environment that is lower crowd and with added festivities. You are there to have open access to MK. The added benefits are special environment theme (like the cavalcades) and special characters around. Boo Bash also adds on the extra perks of the candy and costumes - for a price hike. Boo Bash is best compared to the previous after hours events - or like a super, extra themed Extra Magic Hours with bonus food and character interactions (and price tag to follow).
I have generally heard the price "isn't worth it" from those people. But, they are more event people who can go to MK when they want to go. They wanted all the Halloween Offerings, comparing to MNSSHP (even knowing they shouldn't). And it fell short there. Having short ride lines isn't as valuable to them. If you are viewing this as a very pricey extra half-day at MK with almost a permanent FP line (compared to the normal day crowd level), then it could be worth it.
I hope that gives at least one perspective!