Well... that kinda gets into "what is excitement?". Is it only RWD? Is it only big power and low cars?
I think that "excitement" can be more. It depends on the market. I know that we seem to be RWD people here (hence the aspersions cast at the FWD Grand Ams), but there is a huge "tuner" market out there that either doesn't care which wheels drive the car, or worse, actually LIKE FWD.
And in that case, it's not really all that far off. The G5 is a great tool to lure in the import crowd. Pontiac is into ALMS and drifting now, they just need to start hanging out at NOPI events and start blowing the doors of Hondas in the various events with the G5, and listen to input from the crowd. But above all, don't expect it to be a huge seller (and most of that "input" should be channeled into dealer installable upgrades, since most of these cars are bought on the cheap, or by these kids parents because it's felt that they can't get into much trouble with a civic).
The Vibe, is another good one. It should be cut to only 2 models - the FWD base, and the GT, and the GT should be the AWD model. And even then, the FWD should be treated like the 1LE F-Body option - ignored. People should have to request the FWD model, and little to no mention or emphasis should be put on it. The GT should be AWD and if not turboed, then at least some sort of S/C or turbo should be a dealer installable upgrade. This would compete against the Scion Xa & Xb, the new Imprezza, and the Mazda 3. For those so-inclined, it could be a "lifestyle vehicle" (ala Aztek or Xb), or a cross-over, like the Mazda 3, or a rip-roarin' beast like the WRX and STi. If the WRX can remain in the fight agains the Evo with it's new hatchback form, then the Vibe can CERTAINLY play in that space. Supposedly it's already built to GM spec, so change the spec to focus on performance and move the drive torque to a rear bias with front assist. The WRX should be an easy mark to chase and beat. (so do it the way that the Corvette team tested against a Ferrari and such)
The G6 should probably be dropped. It's a really cool car, but if the G5 takes the FWD, I'm not sure what a larger version would accomplish. However, a RWD G6 hard-top 'vert could be interesting. Could go up against the M-B 230's and Kompressors and such.
The G8 is obvious. Make the V6 the Caddy DI engine, and leave the rest as it is. (well, other than adding a manual)
The Solstice is another obvious one, roadster is kicking ass and taking names, and has all but run Mazda out of the North American market. The coupe should bolster that quite a bit. Be a perfect Exige fighter (in the glaring absence of the Fiero).
Not everyone needs a big cross-over, or little SUV, but... even though I would have said just last week that the Torrent should go, reading the review of gm4life who got one, I may be swayed on that. Seems even that can be "exciting". So why not embrace it and go all the way? Chase the BMW X5 and Porsche Cayenne. Again, AWD with a 50/50 split or RWD bias, and a supercharger or turbo. It doesn't have to smoke the big Cayenne, but it could be the lower cost alternative to it and just get within range of it's performance. (then just work deals with the aftermarket to make Cayenne killers)
But something is still missing.... The Trans Am. It has been aggressive and in your face, and it has been sleek and futuristic. Whether you go with the GTA mentality, or the LS1 WS6/455 SD 2nd Gen mentality, or even the '89 Anniversary path, it's presence is required. Stuff all the gear and goodies in that you can before Cadillac cries, refine the ride like the G8s (comfort with a clear bias toward performance), just with a little MORE bias toward performance. As long as a fully worked out model falls below the base Corvette, it's good. The top dog, the beast for people who want V8 growl and grunt, coupe styling, and every goody and doo-dad out there (whereas the Solstice is about the raw simply driving experience), offer it in T-Top and Hard Top models only, and only 1 or 2 variants (maybe a Formula, and a Trans Am, the former as stripped out as possible, for people who won't by a Solstice coupe due to it's I4 engine).
Acutally, the Holden Coupe 60 is the perfect platform. Put a '78-like front end on it, and drop an LS3 in it and you're golden. People who want to spend less can get a camaro or drop down to the little brother Solstice. The 2002 WS6 Trans Am re-born. Loud, aggressive, in your face, and intimdating. With performance to back up the looks and the bark. (just keep it maxed out in goodies, more-so than the camaro, it should be as KITT-like as possible, that's been the Trans Am's thing since '82)
THAT would be Driving Exitement that is Designed For Action and Fuel For The Soul. Get On Your Pontiac and Ride!