This depends on what criteria you use for "worthwhile". If we ignore interest and inflation, $60 is worth 6-12 DLC packs at $5-$10 each, or three expansions at $20 each, or something midway between those numbers. If we don't ignore interest, then assuming a 5% annual return on investment compounded monthly, that extra $60 is worth about 1 $6 DLC pack every 5 months for the next 5 years, with ~$10 left over at the end of that period. Another equivalency over the next five years would be 2 ~$34 expansions released 21 months apart.
Essentially, if you want to work out the value of the additional DLC packs and expansions that they must release, you need to bring the value back to the value in present-day dollars (I suggest assuming an interest rate of 5% per annum; you can compound it however you want and as long as you aren't assuming things go on too far into the future it won't significantly affect the results). Finding the break-even point is done by what's shown below:
$60 = sum(DLC1/(1 + I/100)^n1, ... , DLCN/(1 + I/100)^nN)
where DCL# is the cost of the #th DLC, I is the interest rate you're using (5% => I = 5), and n# is the number of compounding periods between now and whenever the #th DLC is purchased. You can do this using annuity formulas if you assume that you get 1 DLC per compounding period, too. When the right-hand side of the equation equals the left-hand side, you've found a break-even condition. Since we aren't guaranteed that all additional content will have a uniform price, you have multiple potential break-even points. I chose to assume that it would all be $6 DLC packs; if you assume that there will be three equally expensive expansions released at 1-year spacings, you're going to find a different break-even price, and if you choose to assume a mixture of DLC packs and expansions, all of varying prices, it's quite a bit harder to calculate.
What it boils down to is basically that $60 now is worth ~$77 dollars in 5 years, assuming 5% annual interest. Therefore, if we assume that we get everything we're going to get within 5 years of game purchase, the net future value of all of the stuff we get has to be ~$77 at the end of the five-year period, or the net present value has to be ~$60, for the deluxe edition to be economically worthwhile (this is not including the base game, only the cost of the add-ons, so I'm calculating these things based on the price difference).