If I'm paying $200+ for a CPU, I don't consider $10 a bank-breaking investment.
i5 2500 to i5 2500k = $10 more
i7 2600 to i7 2600k = $15 more
Are you going to make back the 10/15$ if/when you resell it, I can't really say with any certainty.
Is it going to be easier to sell by advertising "unlocked multiplier for easy overclocking"?, I'd say most certainly.
Does it give you the freedom to overclock if you choose at a later date (and with an OC-able motherboard), most definitely.