You could bump up the contrast before saving for web so that it pops a bit more. The most common ways people do this when saving for web is by using a high pass filter, and/or adding a curves adjustment layer with a slight S curve just before flattening.
There's a tut on the blog about high pass filters, and I'm trying to link you directly to it, but it's not working at all. So, sorry to make you scroll but go down to Day 6:
https://www.sweetshoppedesigns.com/i...011/05/page/3/
When you have specified the exact number of pixels (e.g. 600 x 600 or 700 x 700) the resolution is completely irrelevant. Resolution is the number of pixels per inch, but inches only matter when you're printing. Your monitor is going to display 700 pixels as 700 of its pixels, which for most monitors, is 72 per inch. But if you put something higher in the resolution field, it's still going to display the same 700 pixels in the same 700 of its pixels. No change.
Pedantic moment: it doesn't matter how many layers it once had once it's flattened. It could have just been one layer all along, but if it's a really complicated layer with lots of interesting visual information, it's not going to compress as nicely as a solid kraft paper would have. More layers increases your chances for having lots of interesting stuff on the page, but technically, the layers aren't the issue.