Using the Seafoam is a great idea. Normally, what causes your MPG to start decreasing is excessive carbon and deposits in the engine's top end.
SuperChips or DiabloSport would be a good choice.
Air intakes are pretty much the same. Here's a thread that folks contributed to about CAI comparisons you might find helpful:
The bottom line is that you get what you pay for. A good quality, brand name CAI is the way to go. Stay away from the cheapy eBay units that don't specify a filter mfgr. Some of them will come apart and you'll suck filter media into your engine!