Define "better pilot". There are good instrument pilots who have poor stick and rudder skills. There are pilots having good stick and rudder skills who can't (or don't, or never) fly on instruments. They are different skill sets. Some pilots (not many, but some) are proficient, current and skilled at both. There are also instrument pilots who are unable to fly the airplane themselves; if the GPS or autopilot fails, they're dead. They're not pilots, so much as they are "systems automation operators" or "children of magenta" as Warren Vanderburgh famously said. Such pilots shouldn't exist, their lack of skills should be caught during IPCs or flight reviews. But we read about them in NTSB reports, so some must slip through the cracks or find CFIs who pencil whip their paperwork. Don't be that guy!
All else equal, earning the instrument rating should make anyone a better pilot. One evidence for this is that insurance companies typically offer lower rates for IR pilots. But IME, the insurance rates aren't much cheaper, which suggests the safety benefits don't change the risks or statistics a lot. Earning the rating won't necessarily teach you to fly with better precision; maybe you already do. It won't necessarily improve stick & rudder skills either (if you want that, get a taildragger endorsement and commercial rating). But the IR will teach you more about how the airspace and ATC systems work, maybe get more comfortable talking with ATC, and go deeper / more thorough into most of the topics learned during private pilot (navigation, regulations, airplane performance, weather, how instruments work, flight planning, etc.).
If you use your airplane for pragmatic travel, earning the IR might also smooth your trips or improve your dispatch rates. But don't count on that, since in the small, simple, underpowered planes most of us fly, when ceilings & visibility are worse than VFR, there are sometimes other factors that make IFR a bad idea even if you could (strong winds, icing, etc). OTOH, maybe all you need to do is climb (or descend!) through a layer, in which case the IR is perfect and will put a big smile on your face every time you do it. But doing that means being current which requires exercising your IR skills regularly, even if you only occasionally expect to do it "for real".
In short, it might make you a better pilot (depending on how you define it), but it will make you a more educated and informed pilot. And maybe also expand the practical uses for your airplane, if only a little.
