My primary motivation for joining has been that I want to see the sport grow and develop, and for better or worse the PDGA is the only organization I know of that operates at a national level to organize, promote and develop disc golf. I barely play enough sanctioned events each year to pay myself back the cost of membership in entry fee savings, so that's not a big motivator. I would probably re-join in the future even if I didn't plan to play any tournaments in order to continue to support the outreach and development programs of the PDGA. There isn't a viable alternative that I'm aware of.
I haven't used the hotel discounts in past years (have been a member for about 5 years, and most of my hotel business goes to Hilton and Marriott where I have substantial loyalty program benefits) but this past holiday season I did take advantage of it while traveling with the family -- I saved at least $60 over what I'd have paid otherwise, so it more than paid for itself there (particularly since I did play 5 sanctioned events last year). However, there are plenty of ways to get hotel discounts, and in and of itself it's not a significant motivation, just a nice side benefit.
I do like getting the magazine; I'd probably subscribe if it weren't a membership benefit, as long as the cost were $20 a year or less (so you could assign a nominal value of $20/year to that). There isn't currently another magazine providing coverage of disc golf, though there are a number of web sites and such that provide similar sorts of content (this one, obviously -- and I've paid for premium membership here -- but others like AceRunners.com as well). Obviously, the PDGA web site is one of those sources, and I do consider the development and maintenance of that to be one of the significant benefits of membership -- the site has tons of flaws and deficiencies, but it is the de facto central location for lots of information about disc golf.
The other benefits (bag tag, decal, rule book, etc.) aren't that important to me one way or the other. If I were to decide to purchase those independently of membership (unlikely, except perhaps the rule book), they'd be worth no more than about $10 in total.