One of the first posts on this forum that I read and was involved in was some kid who had a myspace domain in an info that was getting phenominal traffic. The owner of the .com contacted him and wanted to buy it. Every one was giving a forumla of revenue x3 years, x10 years, etc. I stuck with 3 as this was perhaps the life (as I saw it) as a popularity factor (now facebook and many others are gaining in popularity).
Even using the three year formula, this was a $225,000.00 domain. The buyer was 15 years old and the seller was 16. They agreed on $49K. Blew me away! It was a true and legit sale.
Anyways, it's like anything else...it is worth what someone is willing to pay for it. If it is a good typo and getting great traffic, it may be best to sit on it awhile and enjoy it.
With all the negative crap going on in the domain world and litigation or people contacting TM holders, don't post it. It seems like it is even risky now contacting the non-typo owner.
The case I gave was not so much a typo but simply a .com owner wanting the .info.
But I think you get the point.
Or not.