A few questions about the 500+ if any of you happen to own one:
(Would rather talk to people who actually have, or had, one, than info from wiki that may be fact or fabrication)
I have two (actually one working).

Did it have any hard drive interface like the 600?
No.
How much chip ram did it come with?
1MB Chip RAM.
Trapdoor expansion slot available and for what?
Yes, trapdoor available for RAM expansions only.
As for the A500 is used for Chip RAM expansion (since you have ECS chipset with Agnus 8375 you can have up to 2MB Chip RAM).
Seems you can use RAM expansions for A500 as well, but I'm not sure (in this case you'll get eg. 1,5MB Chip RAM).
Did it have the side expansion slot like the 500, and if so, was it compatible with the 500 expansions?
Exactly the same.
Any other peculiarities compared to the 500 (other than kickstart and ECS) ?
No... a small tag top of LEDs saying "Amiga 500 plus".

You're welcome!
BY!