I actually do most of my betting on Wednesday, Thursday and Friday and can usually find plenty of value - in fact I usually find it easier than Saturday. When I used to work at the TAB most of the big punters did bet mid-week although the bet value was lower due to the lower pools. Some things I have learnt about mid week betting:
1. Do not bet in very small TAB pools (I regard $10000 as the minimum but 20000+ is preferable) as they are too volatile.
2. If you are a "big" punter then you need to make sure your bet size is appropriate for the pool size - you can't bet as much in a $20,000 pool as you can in a $200,000 pool.
3. If betting with TAB then wait until the last possible moment to bet to make sure your bet price is still available.
4. Be very wary if one TAB is showing much better odds than the other 2 on your selection - you can be pretty sure that the punters will plunge it if they notice the discrepancy (eg. today there was a horse showing about $10 on both Tabcorp & Unitab but $25+ on NSW with about 1 minute to jump when some clown on Sky told everyone it was great value on NSW. With 30 seconds to go NSW had come in to $14 - at jump it was down to $7.50 on NSW but out to about $11 on Unitab/Tabcorp - if you jumped at the $25 looking for value you would have been disappointed (especially since it lost!).
5. You will generally need to look at more than the race form for betting on many midweek races. You get a lot of first starters or horses resuming from long spells which can be great value if you know what to look for. Some country trainers have great records on their home tracks and can give some great priced winners.

Anyway best of luck.

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