My twopenneth on getting bigger gears is +1 for the bigger chainring being the simplest and cheapest way to do. I have a TA rings 61T and 57T.

I would stick with 406 wheels as the tyres are better. I have both 406 and 451 wheels (451 has capreo hub for big gears) however I prefer 406 with the 61T chainring because the Kojak is such a great tyre and the speed/comfort/weight benefits of running kojaks far outweigh the benefits of large gears. You need something to keep the chain on - you can get standalone chain cages that go where the front mech would, or you can get a front mech. When running a big front chainring, run it as close to the bike as possible (for a standard 2-ring crankset that would be in the 'inner' position like on the standard swift) - if you run it too far out the chain rubs on the seatstays in top gear as was discussed a few weeks ago on this forum.

Folding bikes are a compromise - you can't have everything, and spinning out on hills isn't so bad - you can only go so fast downhill before you are going too fast to be able to stop if you had to.