...trying to measure something like gravity waves.
Yep, and that idea will eventually see construction, but it's been shelved because it costs money.
The four MMS Spacecraft fly in a tetrahedral formation to gather 3D data. With one spacecraft, you have a point; two, a line; three, a plane/2D; four, 3D.
STEREO is kinda cool because they use the Earth as another observation vantage of data, in tandem with other input from ACE. In fact, one of the coolest semi-recent developments is people working on solar wind mapping using data from as many current missions (in the solar wind environment) as possible.
Even little sounding rocket projects use ground-based observations to cross correlate on-board instrument measurements with, but I digress. The moral of the story is that you just can't have too many datapoints.
So now, everyone in the industry is currently developing methods of miniaturizing existing and emerging technologies to save mass, power, payload space, and $'s. Combine that with the cubesat/microsat/nanosat developments, and it's just a logical progression; swarms of several hundred spacecrafts that are equipped with better resolution everything instruments.
But hold on there, Hubski isn't /r/futurology. No, our optimism is tempered with at least some measure of realism. NASA will continue to preside over our progression, so you can expect things to continue at a crawling pace. Some issues are solvable with more money thrown at them, but not all of them. Why? Something something bureaucracy, to sum it up. I'll cut myself off here.
Also, welcome to Hubski. :)