If the bike you have is getting the job done & you are happy with it, it's a no-brainer. Repair and replacement of consumables is money well spent.
If you are looking for a more upright bike that requires even less maintenance, a city bike with an internal gear hub is pretty hard to beat. A
Public or a similar
Linus would get the job done quite handily for not a lot of dough.
If your goal is a bike that will be weatherproof for all eternity for not much more you can have an
Amsterdam Bike Company Dutch bike that will be the last bike you'll ever need buy. Passivated and 3x powder coated frames, stainless steel components and rims. Same 7 & 8 speed internal gear hubs as above.
I'm not a big fan of rim brake for all-season, all-weather use. There is a messy sludge that forms and is just dirty and unsightly. Wears out rims and pads unnecessarily. Disc or Roller brakes are preferable for this use. Derailleurs are a whole level of delicate that is just unnecessary in a commute that prizes reliability above all other concerns. Missing a day of work on account of a bent hanger that got tangled in the spokes costs a lot more just a new wheel. A days wages and the hassle and the risk just to find out that the bike shop can't get parts for at least a week just ain't worth it. Others may see the proposition differently and that's ok. The important thing is having a bike you feel good about on a commute you enjoy.