1) The kicker rarely comes into play. A kicker 9 or less is essentially just bad, and I'd call them all top pair no kicker. A2 vs A6 results in mostly ties when there's an ace on the flop.
ProPokerTools Hold'em Simulation
600,000 trials (Randomized)
board: A**
A2
41.75% (107,356 wins, 286,345 ties)
A6
58.25% (206,299 wins, 286,345 ties)
2) Two pair vs. two pair is not a common scenario. This isn't Omaha.
3) Straights with 4 cards on the board aren't getting you paid whether you have A9 on a 5678 board or A2 on a 3456 board. You're playing the connectivity to flop things like a gutshot and an over (to semi-bluff with), or to make straights with both your hole cards.