In using the term "jump the shark" as it was originally designated (in my mind, when a show had run out of ideas, as illustrated by the Happy Days episode), I don't think individual games "jump the shark" for the most part; either a concept is good or bad to start with. Concentration was always a good idea, Burt Luddin's Love Buffet was always a bad one.
The industry, in general, is a slave to whatever trend seems to be hottest. Big-money quizzes that seem easy (with the success of Millionaire)? Sure, bring 'em on. Relationship games? Of course. Humiliating people by playing them for suckers? Naturally. (Side note: it's a great sign that the first episode of the latest Joe Millionaire, which Fox has promoted non-stop for the last few weeks, was a tremendous disappointment Monday, finishing a distant fourth in its time slot and garnering less viewers than Seventh Heaven.)
But that's no different than 30 years ago. Dan, you bring up a good point about NBC-produced vs. G&T-produced Concentration, but the older version looked -- well, old. When it came back with Narz at the helm, I was thrilled to see the nifty update. And, to be honest, I had switched to TPIR at 10:30 in the mornings, because it looked so cool in comparison. (Also, as I've noted here before, the original Concentration opening played to this nine-year-old's mind like something out of a horror movie.)
If making changes enriches the viewing experience -- witness the renaissance of Hollywood Squares under Winkler/Levitt, for example -- it's a good thing. If it detracts from the game -- Card Sharks 2001 being the obvious example -- it doesn't. It takes a little bit of intelligence and ability to go against the grain from the producers to either ride with or against the tide in that regard -- Goodson usually managed to do well in this regard; his successors have not shown the same knack to this point.
(Man, am I on the soap box or what? Must be the baby-induced sleep deprivation.)