With tires there can be a noticeable feel difference, some tires just feel sluggish, usually the more puncture resistant the slower they tend to feel. How much speed difference is something I've never tried to quantify but the overall feeling of a lighter, smoother rolling performance tire is noticeable. With wheels a deeper aero set can get you some extra speed but usually not significant. Two points that often get overlooked is that even if a wheel upgrade means only a .2mph difference, on a longer ride of 60mi by someone who can maintain over 25mph in a group the difference might only come down to around a minute. Good if it means saving the tiny extra energy for the finish line sprint. For a slower rider averaging 15mph the difference can come out to around 4 minutes faster. A good amount of time. The other is that aero is based on an average speed of usually over 20mph but that any ride into the wind is combo of your speed plus wind speed so they can be more advantageous than might be thought by someone who can't maintain 20+ mph. I'd start with tires though and if the speed bug bites, start checking out wheels, don't expect them to magically change your numbers but they will effect your overall results.