So, I was super-critical of the WUP when they first introduced it, because my brain was telling me they were just being greedy. But here was the reality of it all: Waves Sales apparently hadn't been all that in previous years when there were few new plug-ins being delivered to the market by them, more competition exists, and at cheaper prices, and Waves were losing some ground. More, changing VST versions, dropping DirectX support by some, and PT's arrogant changes cause them to work more for less incoming cash-flow.
 
Where I also found WUP terrible was the cost of renewal, which was outrageous! The more plug-ins you owned, the more you paid, and thus the more the company punished you. They've changed that tune for sure, and rightly so. So, there is a maximum charge.
 
Little known trick: Wait until JUST a few days before your first Waves plug-in's WUP expires (since they don't all co-term on the same date). Purchase a 1-year WUP renewal for ALL your plug-ins. What you may find is that the renewal coverage under WUP will cover you for one year beyond your newest, or last plug-in you purchased. If buying all your plug-ins at once, this may not help you, but if you bought many of them piece-meal as I did, you might find your earliest plugin is now covered for up to TWO full years, and everything else in between will all co-term when the latest WUP you purchased expires. It's a one-use thing, maybe, unless you keep buying plug-ins, but it's worth a shot.
 
So, something else to help offset that WUP expense. Watch the sales! Every month, and now, seemingly every weekend, Waves is discounting plug-ins and bundles. Keep a close eye out for these sales. I bought the SSL4000 bundle for a 1/3 of what it normally costs.
 
More, and this is just my philosophy, when purchasing bundles, beware that some of these bundles come with so many plug-ins, you'll find you may not even use a quarter of them religiously. Examine the bundles very carefully and decide if the extra cost really is giving you back all the plug-ins you really will use often. I do envy those who have the Horizon or Mercury bundles, but I've also gone through most, if not all of the plug-ins and rendered many of them just really (and I mean REALLY) good filler plug-ins. 

btw, FWIW, I have the Gold Bundle and noticed in the last iteration of Waves V9r18, Waves tossed in their new Vitamin ($200 value) plug-in. So, for you Mercury, Horizon, Diamond, and so on bundle owners, you're getting an even better deal than piecemeal folks like me with WUP. 
 
Another benefit of WUP in my experience is that, when I was having some really quirky Waves issues in Sonar, Waves scheduled a Support agent to work directly with me at 9PM, since I have a day job away from DAW work. Not only did the agent know how to fix the issue, but he also knew enough about Sonar to fix the problem from how I had Sonar configured.