How can you run the math? Companies don't tell you when and how much they buy back until after the fact.
I'll just lay out an example. Let's say the company is a serial re-purchaser of it's own shares, irrespective of price or value. Let's say that every quarter they buy back 1% of their outstanding shares, and you (as a shareholder) read about this every quarter. So after getting the quarterly, you sell an offsetting amount of shares to bring your holdings back into balance and realize the cash distributed. Some quarters you'll sell near or above the price the company paid, some quarters you'll sell at a lower price. And you were the one telling me not to think on a short term basis? Harumph!
Now, since you mentioned MSFT and DELL back in 2000, let's take a swing at that. Back in 2000, the dividends were taxed as regular income. So, for somebody with a cost basis of $50 in the 35% tax bracket, every $1 returned to shareholders via repurchase would be recovered on a tax-equivalent basis at a selling price of $32.50.
Yes, so while you might not necessary sell at the same price the corporation paid, you have a lot of room to go down -- potentially all the way to $32.50. Other people with a higher cost basis would the added advantage of getting a tax loss, and some would be looking at a capital gain... but the capital gains rate was lower back then (relative to the dividend tax rate).
So it depends on a few factors... dividend tax rates vs capital gains tax rates, and cost basis being an important one. But the serial repurchaser of shares will give their shareholders roughly equal chances to sell at lower or higher valuations over time. Like you said, don't think short-term about this.
And I completely don't buy into the theory that buybacks at any price are good.
I'm not saying they are good either. I'm just saying it's not really much different from paying a dividend, provided you sell some of your shares to offset your increased ownership.
I'll be the last one to bitch and moan if the company is willing to buy my shares for a high price. Like... that's probably the least of my complaints about management!!! Would somebody (anybody) please pay me at least full value? I really don't mind who it is.