I just finished my second full playthrough after consulting a few guides to figure out what I'd missed on the first playthrough. This guide from sierrahelp.com only lists 424 possible points you can score but admits to being incomplete, also there's a certain item on the list that makes me think it was meant for an earlier build of PQ4 before the CD version came out (picking up and using a stick instead of the pry bar to open the steel doors leading to the killer's lair).

The most comprehensive guide I've found thus far is here, leading to the collection of 503 points. One user on an old gaming forum claimed to have scored 505 points. Today I managed to score 508! 2 of the points missing in the second guide I linked come from giving pretzels to the dog in Griffith Park on the second encounter (use your broken mirror on it the first time, or perhaps give it pretzels the first time and use your mirror on it the second time and you might possibly still get all the points). I haven't put any time in yet to figure out where the remaining 3 points are from, but I'm willing to look into it if anyone's interested.

How about you guys? Anyone else reached 508 points or beat it?

By the way I just want to add, the way DOS games are typically set up with GOG, the sound quality and hardware emulation are beyond terrible. I highly recommend using a program like RetroArch (with the DOSbox core) to provide better options including Roland MT-32 emulation, also you will probably need to tweak the game’s basic sound config by either re-running the DOS installation/setup program (if provided by GOG) or else editing the appropriate config files by hand.

With Police Quest 4 it’s probably sufficient to just tweak RESOURCE.CFG in the game’s installation directory and set “soundDrv = GENMIDI.DRV” to enable the Windows general midi driver to provide the music playback, but there are many other sound options you can go with and will want to utilize, especially with older titles released before the general midi era.

For those that don't feel comfortable editing the resource.cfg file (or creating it if GOG removed it), then they can always just use ScummVM and setup the sound options through there

I'm a purist so I tend to prefer DOSbox, especially since I hear that certain things will behave slightly differently in ScummVM than in the original versions, but I hear ScummVM is much easier to use with the games it supports and I'm planning at some point to try it out myself. As I understand it, another big advantage of ScummVM is much lower CPU overhead due to the more efficient and direct code translation for modern systems, so it could definitely be a good option if you're struggling to get decent performance in DOSbox.