If that were my bike I would keep riding it as is. The things that would be cheap and perhaps make it a bit nicer might include:
koolstop salmon brake pads for better stopping power

new cables/housing for the brakes -- not sure what quality these things are on that bike, but many department store bikes really cut corners on these and could impact braking power

if the shifting is not so great replacing cables and housing could help here

a nice set of tires

Next year you might be ready for some of these consumables -- replace them then. Save you money and a year or so from now buy yourself a better bike. If you start watching Craigslist, and are not in a hurry, you will have a good chance of finding a gem for a pittance.