Unknown location solved? The movie theater where Crockett & Billy watch the Frankenstein flick.
The walk scene Crockett & Billy before was filmed on 600 block of Lincoln Road Mall, as also confirmed by CGlide on his location page. http://www.miamivicelocations5.org/page21.html
The Movie theater afterwards is still unknown, but it is very likely that this was the Colony Theater at 1040 Lincoln Road. http://cinematreasures.org/theaters/3085/photos/215097
Of course, it is hard to prove that, since the scenes with Crockett&Billy show only seat rows and no decisive clues from the surrounding or the entrance. But there is a short establishing shot with Billy sitting in the theater at first (see picture below) and this picture matches with the overall size and approximate seat pattern of the Colony (second pic below), even if the theater has been renovated since then and looks more modern now. In the episode it looks very aged.
Crockett& son sit in row 6 with 13 seats in total, 11 rows visible in this shot. There are two main aisles with another two blocks of seats of the same size (would add up to 429 seats in these three blocks in total assuming three identical blocks, which nearly exactly matches the historic seat capacity given with 465). The theater seats are ascending which is not the case in all other old movie theaters. In my current picture the rows are also ascending, but there are 11 seats per middle row, but the seats look broader and the aisles too. A second picture of the current state is here to confirm which shows 374 seats total capacity in 17 rows and 3 blocks with the outer blocks being smaller and only 6 seats per row).
I am 90% convinced by the layout and the location logistics argument in this case (they rather filmed the walk at Lincoln Road because of the theater location and not vice versa). What do you think?
P.S. of course I checked other theaters too but they disqualify. The Lincoln Theater that was at 541 Lincoln Road and therefore exactly next the filming location of the walk in this episode, was closed between the early 80s and 1990 when it was renovated for 1+m USD., so it could not have been used for filming in Dec 1988. Another fact speaking in favor of the Colony is the 465 seats total stated which matches approximately what we see in the episode (bear in mind that the 465 relate to the time when it was a movie theater. It was restored afterwards and rebuild into a performing arts theater with stage). The Lincoln had 750 seats.