Would you rather:

1) Pay me $1,000. I generate a random number from 1 to 1,000. If that number is 523, I will pay you $1,000,000,000. You can keep playing as many times as you want, but after you play a few times the reward drops from $1,000,000,000 to $500,000,000

2) Take $1,000 I give you for free right now.

See the problem? If you are unlucky before it drops to 25BTC/block, you CAN NOT expect things to average back out in the long run. You COULD get lucky in the short term too, but then your EV is the same as (not better than) solo mining. It's a question of whether you think the implicit fees you mentioned are worth the fact that you might make losses that will not be smoothed out by the law of large numbers after block payout changes.

EDIT: Wait, or would the probability rise to 1 in 500 at the same time (in situation 1)? In that case, nevermind, but:

The logical extension of your mentality about this is that you shouldn't buy health insurance because you would pay more per month on health insurance than you would on average spend every month on paying for your own healthcare when you get badly injured.