Yes, you get to enter
Disneyland 3 hours before party start time.
I would certainly plan for crowds, even if you weren't going to the first party. The first party historically sells out, but historically, many (most?) parties have also sold out. So in theory you'd be dealing with about the same number of people on most party nights.
Reports on crowd levels are very mixed, but few people say crowds are "light." For many people (myself included), crowds were heavier than expected, given you're buying a separate ticket to get into the park for a party.
It sounds like you probably like Disney Halloween parties.

So I think I would probably go if I were you, if for no other reason, just to see the differences.
In general I would recommend the party to people who are interested in at least a couple of the following (or VERY interested in one item): wearing a costume at Disneyland, special meet-and-greets, dancing with characters, villains, villains-themed fireworks, trick-or-treating, interesting fog/light effects, and/or a SMALL parade (much smaller than WDW's).
You will be able to ride rides as well, but they're the same rides you would have experienced outside of party hours. I would never attend the party counting on reduced crowds or wait times. Some rides will have short waits, and I think most or all will have shorter standby waits than they do outside of the parties...but those rides are the ones you could have gotten a FP for on a normal day and probably had a 5 or 10-minute wait instead of a 30-minute wait.
The people-watching while waiting in line, however, is much more interesting during the party.

You could probably add peoplewatching to the list of fun things during the party, but most folks come in before the party officially starts so if you just want to look at other people's costumes you could do a lot of that without buying a party ticket.
If the "perks" don't sound great to you, I'd either save my money/spend it on something else, or (if you can be in the area near park opening on Friday) just upgrade to a 3-day ticket for Friday ($50, I believe). You can experience DCA and/or DL early in the day. DL will start to get more crowded than usual 3 hours before party start time, and DCA will get
very crowded close to the actual party start time as everyone who didn't buy tickets migrates to DCA. With Cars Land, though, an extra day for DCA has some appeal, even if crowds convince you to leave before DL's Halloween party starts.
Have a great trip!