What's your target device- mobile or desktop? I have little experience in mobile, but with desktop you'd be pretty safe to look up the most common resolutions and aim for visuals which will satisfy the most people. The Steam hardware survey is great for this and, well, I'll just tell you what it shows: Most people have one or two 1920x1080 monitors on the high end, but there's a significant number of laptop users at 1366x768. Those two resolutions are pretty much what you have to target, aside from a few (vocal) enthusiasts with super premium displays.
How do you feel about upscaling and seeing the pixels? Sounds like you're not of fan of that approach. Leaving it to some other sort of filtering is probably not going to look good unless you're really careful; imagine seeing little blurry bits contrasting with sharp bits all over depending on how something was rotated or scaled. I wouldn't advise it unless you've got a sound plan to handle rendering.
Perhaps you think of some examples of games whose visuals you like? When I think vector graphics, I think of World of Goo (for example), which did pretty well. Simulating the look of vector art with large raster files is, I think, inefficient and will almost certainly create weird scaling artifacts. And if you can work around that, you might as well have made the graphics vectorized and done effects in rendering.
... The more I think about it, the more it sounds like you want to do vector graphics based on what you've written. I actually don't have any practical experience doing vector graphics for games, so I'll just leave it at that thought.