I'm guilty of watching something or wanting to watch something because there is a Whedonverse connection, no even gonna lie. I don't necessarily own anything because of that connection, however... Unless you want to look at Shadow Puppets, which was all about James Marsters.
I saw PS, I Love You because of James, also... and I loved it, even though I've never been a Hilary Swank fan. Honestly, I hesitated seeing it because of her... then of course, I found out Jeffrey Dean Morgan was in it too, so I had to watch 😉
I love the American Pie movies, but that did not stem from a Buffy thing. Although, How I Met Your Mother totally did... and the only reason it had staying power was because of Aly and NPH (although I'm feeling a little less than satisfied lately... I think it's gone downhill a bit).
I loved Bring it On, and Eliza only helps that... and of course I own Tru Calling and Dollhouse... And then there's Bones, which initially was all about David Boreanaz for me, but now it's such a great show, and he makes it great, but even if he didn't have that Buffy tie, I would still love it.
Typically, I have no interest in owning something unless I absolutely LOVE it (Shadow Puppets excluded... I liked it the first time around, and never watched it again). Buying and owning movies/tv shows is like an investment. If I'm not going to absolutely love it and watch it thousands of times, there's no real point in owning it... just saying.