Flashes are designed to illuminate focal subjects at a near-mid field distance. You have very little control over the exposure across a whole frame and taking into account depth of field, as the light from a flash is a single source pulse that diminishes rapidly with distance. Obviously they will give you extra light to take photos in dark places, and they're an improvement over any on board camera flash (in that they will throw light further, and you'll get less orbs, dust etc), but not much more than that.
Similarly a low f/stop lens is great for letting more light in, but when you lower the f/stop you lose depth of field, so that is also very situational and inflexible. A low f/stop prime lens is an excellent investment as you can take awesome photos with them, but they're not a viable solution to low light photography.
I can guarantee that 95%+ of all the photos taken in darkness that make you go *wow* on here have been light-painted with a tripod, long exposure (sometimes 5+ minutes) and torches. Sometimes practice, perseverance and some tricks can go a whole lot further than throwing money at kit, which unless you learn to light-paint most probably still wont give you the results that other people get.
Ultimately it doesn't matter so long as you're happy with your photos. It's all subjective. My point is you don't have to throw money at kit to get good photos, and if you do it might not work. Much better to learn all the tips and tricks until you feel your kit is the limiting factor, THEN it's time to upgrade.
As I said right at the top, this isn't a photography forum, and you're better off asking the question on a camera/photography forum of which there are many filled with pro experience.