Re; Very high TC plays
"Is there ever a TC high enough to make it worth while to split 10s against a dealer's 5 or 6? What about doubling on a soft 19 or 20?"
Yes & they're not that high: split 10,10 v 6 @+4, v5 @+5. DD against 6 or 5 with soft 19 only requires + 1, & with soft 20 +4, +5 respect.
(assuming you're counting 2,3,4,5,6 +1, 10,A -1 & dividing by full decks remaining in a shoe game)- See, & preferably buy Wong's Professional BJ (Table 9.)
"Would these just draw attention"
Yes they probably would, most counters ignore them for that reason.
"or are they possible plays? Where i play, lots of players make "unconventional" (read bad) plays and no one bats an eye."
Yes, but worry only about how the house will view you. Such plays would suggest you are either an idiot or a counter. If the pit sees your other play is solid, they may elect the latter view.
"The idea came to me last session during high count. I know your not "supposed" to split 10s, but if the count is high enough and the dealer is showing a 6, you are already in a very advantageous postion. Wouldn't it be a good idea to get more money in play during such an advantageous position?"
Short term, theoretically yes, (these plays will increase your fluctuations though) Long term if they raise unwanted attention, no.
Realise to that at the given indice numbers the play is only marginally better than basic strategy, so the profit is not that great until the count is higher, & even then as a % of the overall profit is not that important. Splitting tens ofetn upsets other players who do post mortems, reconstucting their losing hands as if you hadn't split. When this reconstruction shows they would have won they are often unhappy & will let you know :)
See Anderson's Burning the Tables for excellent discussion on which plays should be avoided for longevity.
"And even if you hit small cards, that leaves even more more high cards in the deck for the dealer to hit. (is this last thought logical?)"
I'm not an expert, but sounds right. I wouldn't focus too much on what you can't control.
What I don't understand is that you're counting but don't know indice numbers for varying basic strategy. Admittedly knowing when to bet is 75% of the money.
75% of the remaining 25% comes from 3 playing deviations (Wong or Anderson-I can't remember), stand 16v10 @ 0 or positive, take insurance at +3, stand 15 v10 @ +4 (table 9 again)