I replace everything I can on every bikes I have, on some MTBs it's surprising how much weight you can save but durability and resistance to fatigue is the real game changer here... Gold and oil slick looks good too 😂
Yes, titanium bolts in an aluminum frame can cause Galvanic corrosion. Although proper maintenance can help avoid that I would highly recommend to put some grease in there at least something to help keep water out of the threads
