There's a good amount of space above the intercooler, but it would take more work to utilize. When I upgrade my intercooler I intend to move the pressure switch on the condensor to the backside, the horns to another place and the A/C receiver/dryer to near the battery. This way you could just weld a second Viggen intercooler above the first one. (making a double core intercooler is probably the cheapest way to get more flow) If one flows at least 230 hp, two should handle over 400 hp with the appropriate hoses etc. And doubling the forward facing surface area should help with cooling more than just making it thicker. PLus a new Viggen intercooler is under $300, just add the cost of welding and moving everything else, and for under $500, and bit of work, you've got a 400 hp intercooler. Of course I won't be doing this too soon. I'd imagine such tampering would easily void one's warranty. But for other 9-3 owners this may be an alternative to moving the condensor (which would only allow a slightly larger intercooler) and to removing the aluminum bumper piece (which would be a disaster in an accident). Once two were welded together you'd be looking at an intercooler core measuring about 2.5" tall X 21" wide X 15" tall. Lots of flow and lots of cooling, and if you're any good at welding, doing away with the plastic ends should easily allow for plenty of boost without cracking.
Also, if you don't mind removing the metal bumper piece instead of what I listed above, doing so would allow a second intercooler core to be welded in FRONT of the existing one. Doulbing the flow, and still dramatically increasing the cooling again for less than $500.
For examples on making multiple cores go here:
www.relentlessracing.com
Click on "intercoolers" on the left hand side.
A double core Chrysler intercooler will flow roughly 650 CFM. To give you some idea how much airflow that is ... the stock Aero turbo flows only about 428 cfm. The upgraded 18T compressor flows less than 500 cfm. If you live on the east coast relentless racing might even do the welding for ya. Anyway, new intercoolers look nicer, but if you want fast AND cheap. Multiple cores might be the way to go eh?