The problem is once you start adding things like this to the game then it often becomes what the game is about.
I found my 3.5e games got bogged down a lot by small modifiers that weren't all that complex. But there were so many of them and they were such a small bonus that they tended to get forgotten on a regular basis. Whenever someone forgets to apply a modifier, however, my players love to point out how much smarter they are to the other players so that was all combat ever became:
Player 1: "I trip the monster. (rolls a 12). That's 20 total."
Player 2: "Wait. I know you have a 16 strength and a 5 BAB, so isn't that 22?"
Player 1: "Plus 3 for strength, plus 5 for BAB. That's 20."
Player 2: "Aren't you using a flail?"
Player 1: "Yeah? So what?"
Player 2: "All flails give +2 to trip attempts."
Player 1: "What? I didn't read that."
Player 2: "Yeah, it's right here. Flails give +2 to all trip attempts."
Player 1: "Hmm, I didn't realize that. Fine, then it's 22."
(Next turn)
Player 1: "I trip him again. (rolls a 10). That's 18 total."
Player 2: (only half paying attention to the roll) "Did you add the flail modifier?"
Player 1: "Crap. I forgot. That's 20 then."
(Next turn)
Player 1: "I trip again. (rolls a 10). That's 20 total."
Player 2: (only half paying attention to the roll) "Remember flail?"
Player 1: "Yes. I rolled a 10, plus 5 BAB, plus 3 strength and 2 from flail."
Player 2: "Ok, ok. I was just making sure since you forgot the last 2 rounds."
Then repeat this process for every modifier in the game....in every round of combat in the game.