It really depends where you're staying, and unfortunately it can take a modest amount of research to know what you're getting. For starters, there are some properties that don't accept SUA, so it can be disappointing when you've picked out a hotel only to find you can't redeem an SUA there. The list isn't huge, but contains some notable properties in popular cities.

Then there's the fact that some properties' standard suite (the only type of suite you can redeem the SUA for) is arguably a poor room. For example, there are some tropical destinations where using a SUA will get you a "resort" view rather than an ocean view, which for a lot of people is a notable downgrade (e.g. Andaz Maui) .For some others the variety of sizes and configurations in standard suites can result in a chance at a very marginal actual upgrade over a normal "deluxe" room upgrade depending on luck of the draw in which suite you get (e.g. Andaz 5th Ave). In many other places, a suite is just a very small actual upgrade due to properties migrating their rooms from true suites to "junior suites", which are really just a slightly larger normal room. Depending on where you're going, the value proposition of SUA vs. having taken the 5k points can certainly be dubious. So things like this mean you'll often want to research the details of SUA at a given property before redemption.

As you say, booking far in advance can be necessary at popular destinations. Places like GH Kauai can sell out of standard suites within days of calendar opening 13 months in advance. Now that awards can be transferred, high-demand properties are seeing their standard suites being gobbled up even faster since non-loyalists are getting awards from family/friends or buying them on the grey market.

In general I think the likelihood of getting great value on 6 SUAs within their validity window isn't easy. One trick is to try to hit your SUA milestones after October 1st since you get 90 days to choose your milestone award. If you select SUA from your milestones after Jan 1 of the following year, the SUA don't expire for ~2 years, giving you more time to find value. Especially true if you don't think you'll be earning many/any SUA the following year.