Yeah, you have fairly easy plants there.
Hairgrass will most likely die off though. I've never had much luck with it even under T5s, flora base substrate and weekly dosing of fertilizers.
RE upgrading, it all depends. What plants do you want to keep? There are low light plants that will grow perfectly well under what you have such as java fern, java moss, most Crypts, Anubias, hygros, wisteria, valisneria, etc. Look up plants, decide what you like, look up their requirements and decide if it's worth purchasing T5s.