Should I?

That's a tough judgment call. What may be best for me or for others, might not be the same for you. I would suggest watching the series to the end. You might always wonder, "What did happen?" You could then post on the threads, "What happened to all the characters after the show ended?"

SPOLIERS:
If you finish season 7, you can see the writers and producers are PO'd with Topher for leaving the series. They turn Eric into a simpleton caricature of himself. The first half of season 8, they totally trash Eric's character, even with him not being there.

They also bring in such unnecessary characters like Randy and Samantha. In the second half of season 8, the writers/producers figure out their mistakes and try to find ways to write Randy and Sam out of the series. Just my thoughts and my opinions.

My personal recommendation is to watch the entirety of season 7, but don't bother with season 8. There's no one juncture in season 7 where it makes sense to stop watching, and I think Eric's sendoff in the last episode is important. There's also some good Jackie/Hyde stuff in season 7 despite what happens at the end of the season.

I caught a few scattered episodes of season 8, including the premiere and the finale, on The N long before I watched the whole show start to finish, but beyond that I never watched it for the same reasons you expressed and I don't ever plan to. It's not so much that the quality of humor is vastly inferior to the preceding seasons, since I think most would agree that the show was clearly in the decline from season 5 on, but the characterization is way off. With Eric (the heart of the show) and Kelso absent and the rest of the characters getting butchered in terms of development, I really don't think it's worth seeing. As far as Jackie and Hyde, it's mildly infuriating what happens to them. I'm not so much of a rabid shipper anymore that I can't deal with them breaking up, but the utter lack of regard for the fact that they even had a relationship is really irritating. Like, you know how when Jackie and Kelso break up, you can still tell that they had been in a relationship? There's no sense of that whatsoever with Jackie and Hyde; it's like one episode they love each other and the next they're completely indifferent to one another. Really terrible writing. Even Danny Masterson says that season 8 is a joke.

Watch the whole thing if you want to be able to say you did—you won't be traumatized or anything, lol—but I don't think there's much to gain. Season 7 isn't a perfectly satisfying end to the series, but was better closure for me than season 8 would've been.

I love the show and I have no issue with season 7 at all. Season 8 isn't awful, but far from as good as the rest of the show. I've watched it several times and still love it just as much as the show has a good finale despite the bad last season