those are nice looking ski's but a tad overpriced IMO, although i'm not that familiar with MI prices.... however i've argued in the past that sometimes overpaying for the right ski and getting lucky with a couple seasons of trouble free riding more than offsets the additional cost. I love the 96 xp, had one just like it and put a lot of hours on it, still kind of miss it, its one of my favorite two strokes. (Gp1300r Yamaha, 96 XP Seadoo, 99 GSX Limited Seadoo in that order)
the 787 is generally considered reliable, you will still have access to plenty of good used parts, relatively easy to work on for those mechanically inclined, pretty easy to diagnose, and lots of proven repair methods are posted on the forums. Those ski's are really only designed for 1 person and there is a bit of a learning curve, but nothing that 90% of the people find troublesome except for limited fuel range, 40ish miles on a full tank (9 gallons) is about all you can safely plan on.
With that said, two sparks will certainly prove to be more reliable, just as fun, and significantly increased fuel range (double) and have a little bit more of a cool factor, and the huge bonus of the warranty, and from what i've seen so far, minimal depreciation...
so... a couple xp's will certainly get you a nice "starter set" that will be an absolute blast to ride, there is minimal depreciation since you're already near rock bottom (especially if you pay to 3K vs 4K) you might invest $150 in a couple set's of hydroturf and some decals and they will be even better looking... (I hate the stock mats)
note: Michigan's season is about over, there WILL be better deals coming up when the weather turns.... but i'l circle back to my opening statement, the right pair of 2 strokes that have been well taken care of will offer a lot more enjoyment, and better value than a troublesome pair where one is always breaking down and ruining a saturday. So going the clearance puppy route isn't always the best unless your the type that enjoys tinkering. Those two you linked look very clean on a quick glance, but trusting the seller is critical as well, good compression, the right oil, zerking the zerks, all parts working like trim, replacement fuel lines, clean rave valves, access for a test ride, etc... all factor into a ski's value and projected reliability.,
bottom line, you can't go wrong either way, the xp will give you lower entry price but higher chance of hassles. I have always suggested that people get in cheap and find out if they really really like the sport before they decide to make an upgrade, no point in spending 11K vs 4K only to find out that the novelty wore off and then you take a hit on the sale.
I've had several friends try it out and decide they'd rather golf, but most of my friends tried it, loved it, and still love it.