There are 3 reasons I'd buy a SVV mandatory week:
a) I loved SVV and wanted to lock in a really hot week, such as Christmas, 12 months in advance so I wouldn't have to stress over an II exchange.
b) I didn't have or want to spend a lot of money to buy WKV, but I really wanted SOs.
c) I also wanted to enjoy Starwood advantage in II with a minimum of dollars spent.
I own an EOY SVV because I had a VOI worth 148,100 SOs and wanted to have enough SOs to get into a 3 bdrm at WSJ during platinum plus season. I could have bought WKV, but I wanted a low-cost alternative because having enough SOs to exchange is not the same as actually being able to execute such an exchange. It's all subject to availability, you see, and the last thing I wanted to do was to spend $10k on an experiment.
So I'm a minor fan of SVV, even though others pooh pooh it. Not everyone wants to spend $15k on a WKV plat 2 bdrm, you know?
Now, there are a few things you need to know. First, is that unlike a lot of resorts, SVV has 2 types of 2 bdrms, a lock-off and a regular 2 bdrm. The regular 2 bedroom platinum units are worth 81k SOs, while the lockoffs are worth 95.7k SOs. It's an important distinction because if you want to do II exchanges, only the lockoffs can be split into 2 separate deposits. You cannot do this with a regular one bedroom; you either use the whole thing or deposit the whole thing. That's a downside to owning the regular 2 bdrm.
Also, note that if you want to visit WSJ, 95.7k x 2 = 191,400, which is enough to get you into a 2 bdrm at WSJ. 81k x 2 = 162,000, which falls short.
As far as II exchanges go, you are correct that SVV isn't going to get you very far except for other Starwoods. With the Starwood priority, if you play your cards right, it will probably get you into WLR and WKORV during shoulder season, HRA during low season, SBP, WKV and SDO during shoulder season, and Orlando pretty much year round. I highly doubt you'll ever see WSJ, HRA or WKORV in high season (whenever the kids are out of school), or any of the Colorado ski resorts in winter.
But because Orlando resorts are so plentiful, I doubt you'll ever get a great non-Starwood exchange, such as Four Seasons Aviara. I honestly don't know of any hut-on-the-water type timeshare resorts, but I highly doubt it'd be strong enough to pull something like that.
But owning any Starwood timeshare will get you access to II Getaways, which can be really good deals. If you can travel in shoulder season, I've seen resorts such as Marriott Aruba, Marriott Ocean Watch, Marriott Surf Club, Marriott Canyon Villas, etc.