It really is a toss-up. The SD700 is 6 megapixel and the newer ELPH 100 is 12 megapixel. That sounds like a big difference, but for most purposes, the difference between the two is minimal. The lenses are about the same, although the ELPH 100 will be able to zoom out to a wider angle than the SD700, which would be useful for general day-to-day photography. But they occupy pretty much the same product category... one is just a few years newer. Image sensor and image processing improvements have continually gotten better during that time, so overall I would expect better results from the newer camera; however, for your needs, I don't know if there would be much of a difference. It really comes down to how much you want to spend. For under $50, the SD700 is a great buy. If you want to spend $125 or so, the ELPH 100 will produce great photos -- definitely better photos than the SD700 -- but maybe not enough difference for you to really tell, or for it to be worth paying 2.5x the SD700.
That being said, $125 is still pretty cheap, and the ELPH 100 has a nice solid feel, and it is appreciably smaller than the SD700. It is smaller than, say, an iPhone, or most mens' wallets. The SD700 is in the "small" category too, but it is definitely a bit chunkier. I think the SD700 would be thicker than an iPhone, while the ELPH 100 is about the same thickness or thinner.
The G7 would be substantially larger than either. Most G-series cameras will fit in a larger pocket like a jacket pocket, but they will never slide into a front jeans pocket like the SD/ELPH lineup.
Any of these (whether an older, more expensive one, or a newer, cheaper one) will not be "professional" per se but they will be leagues above the camera that you have now. They will all be about the same in terms of ease of use, etc. The G7 might give you a little better photos, but at the expense of some size and weight.
I really would recommend that you go to Target, Walmart, Staples, Office Depot, Sam's Club, what have you... they all carry the ELPH 100. Hold it in your hands, take a couple of photos with it, put it into macro mode and see if it focuses close enough for your needs. The SD700 would be pretty much the same, only a little bigger, and not quite as capable when it comes to the photos.
It actually looks like the SD700 can focus closer: Canon states 0.79 inches close focus distance. That is pretty remarkable. The ELPH 100 is 1.2 inches. So you can get close-up photos about 1/2 inch closer with the SD700 than with the ELPH 100.