Wattage is the wrong question.
A good quality 25 watt iron will do much better than a crap quality 30 or 45 watt one. I use a Weller WP25 and love it. It costs around $30-$40 and is A LOT BETTER in so many ways than a Radioshack cheapy. The tips are better, it heats up faster, more comfortable, the list goes on. Of course, at 25 watts it struggles just as much as the Radioshack cheapy with some things. But for portabilizing, it's great. Get an ST7 or similar small tip, the stock one is MASSIVE.