Baseball been bery bery good to me
This is a picture of a published game designer
1) Is it a bad idea to deliberately play for a tile-exchange? I often find myself lining up an exchange a turn or two early - do you think this is compromising my overall strategy?
That depends. Late in the game you should definitely be playing your low colors. Early on, you go for just the biggest numbers. When does the shift occur? A few turns before you realize it.
2) Playing for the Ingenious bonus is hurting.
You want big numbers and you want to score your low colors, but getting Ingenious is not always useful. If you have 15 or better in a color it is usually best not to score the Ingenious until you have a combo that screws up your opponent. Eg, if your opponent is low in green there is a long line of green open at both ends, you might block one end of that line with your move that scores Ingenious and then block the other end with the free move.
3) Is it possible to play too defensively?
Yes, but with two players it's not common.
About halfway through the game, I identify my opponent's weakest colour (possibly two) and try to cut it off. This, though gives her more opportunity to do the same to me.
It's a question of balance. You want to block your opponent's low color, but not at the cost of getting your own low color blocked.
Is it possible to try and block out one colour right from the start?
No, but once you have a significant lead in a color, you might try blocking it.