Same as Yax, I've been member some decade ago for some 5 years, so I can only speak for that time. All the perks mostly have to do with their live gigs and considering current situation - I don't think you'll use any of them soon.
In those 5 years, several times I bought tickets before they went on sale (and those areas or shows I bought were sold out on the day tickets went on public sale). Three times I've won FTTB (First To The Barrier) and I say, that's a huge bonus. And most important of all, back in '08 I've won Heaven Can Wait - once in a lifetime experience. So looking back, considering only things mentioned above - it was definitely worth it.
Back at that time magazines were so-so. Most of those featured articles I had no interest in (interviews with guitar technicians and similar). Also, they were late, like really late. The deal was 3 magazines a year, but with time they were so far apart, I believe they owe me at least issue or two. I hear the situation is better now (both with the delivery and the content inside of magazine). I didn't order much from official fan-shop so I can't really comment on the discounts.
Also, those exclusive products? Those rarely came and even when they did, after some time they went public (personalized shirts for example). Resubscription shirts were hit-and-miss. Some of them were awesome the rest of them I had a feeling they did them only so they could say they've done their obligations. Monthly prize draws? Forget about those. There is one item per months and the items were really cool, tho, vinyl signed by the whole band, for example. But considering the number of people paying membership your chances are really low. You would also get a welcome package before (with "signed" photo, welcome letter, Steve Harris bass pin and some other things but I noticed they don't do those anymore.)
To conclude, in my case, it was definitely worth it but none of the perks were material (merchandise) based.