A big bore kit and/or hc forged Pistal pistons will add some nice torque and throttle response down low, it will also smooth out power band in the 3-6k range which many find useful as a street bike. Transition from partial throttle to full throttle at nearly all speeds is also improved. Engine braking will also be increased. It should also be noted that some of the same can be accomplished with lighter flywheel for substantially le$$, although w/o the gains in max. torque output of course.
If you're looking for more hp, it depends on how much. The stock head porting will only flow efficiently up to around 7800 revs, witnessed by the published hp curves and Ducati's claim of max hp occurring at 7750rpm. VeeTwo of Australia does offer a hotter cam that adds 20* of inlet duration and substantially higher lift on both intake and exhaust lobes. The cams are available individually or in a kit including the 98mm Pistal hc pistons and barrels and cpu mapping. The kit lists for something around $1,800 USD and shows the obvious big increases in torque, however only 8 hp gain, peaking at same rpm as stock. This kit alone seems to offer marginal value, at least if you're seeking gains in hp. I mean we're increasing displacement roughly 8% and netting a hp gain of roughly...8%. Now obviously if the engine were able to breathe efficiently at higher revs, those lumpier cams could actually do there intended job and we might see some REAL substantial hp gains. Guy Martin claims with proper porting of 1000DS heads, including installation of 47mm intake, 41mm exhaust (stock is 45/40), some reshaping of combustion chambers AND the hotter cams AND the big bore kit AND the remapped ECU, these motors could actually produce 115hp at the rear wheel! That folks is 999 territory. Of course the cost for all these goodies, along with of course an open air box and free breathing exhaust, would be in the $5kUSD range.
The good news is that the SS chassis could easily handle the power gains and the resulting bike would likely have a better power to weight ratio than a 999R. I'd be a bit concerned using stock body work about cooking that rear cylinder, probably a good idea to strip off at least the lower cowl fairing, maybe even turn it into a streetfighter looking bike.
If you were concerned about getting your $$ out at some point down the road, I'd probably tell you to get a SBK, I think most buyers would balk at paying more for a used SS, no matter how tricked out, than for a new version of same. I'd also probably not recommend such a kit upgrade be installed in a Monster, SportClassic or MTS as I really do not think those chassis' are up to the task of handling the torque or top end of such a beastly motor. The biggest downside of such a project, besides the cost of course, is there appears to be no intermediate steps to acheiving the end result. Installing the VeeTwo kit alone w/o proper porting seems to net minimal returns relative to cost and future porting would once again require bike and motor disassembly.
If you proceed with this project, keep in mind you'll also need to upgrade clutch springs, possibly install a slipper clutch and Nichols flywheel as well. A crank balancing ($250) and Carillo rods ($600) would also be added to itinerary if it were my bike and I planned on getting to that high revving power band often. If you do indulge yourself in such an endeavor, i certainly wish you well and hope the end result is what you were after. Please post dyno numbers if possible, including a baseline value for your stock setup prior to project, if possible. Take care.