I personally would use whatever the system is set up to use.
There's nothing wrong with higher numbers, and the math can work just fine as long as everything is designed to work together. That said, if the math assumes that you have a weapon of a certain bonus, it certainly changes the nature of magic items in the game. It means that you need to keep such items fairly accessible. It also means that you discourage the use of switching between weapons, implements and the like, as you either need to keep multiple magic items around or miss out on the bonus part of the time.
I think the game should assume almost no bonuses to hit and defenses from magic items, and if that's the case each additional +1 should be increasingly rare. If the math of the game functions according to you having no such bonuses, but you actually have +3 to all attack rolls and +3 to all defenses, that represents a huge shift in balance.