I don't think it credible or likely that a name like Namibia.de
actually sold for $35K, regardless of what may have been
reported...
The truth is, some non-hyphenated geo '.co' names could
resell for a decent price, but there is no real market for them
and I personally think that buyers of these particular domains
are making a mistake.
The 'mistake' shows its face when a viewer looks at the domain,
then at the TLD, and sees an obvious discrepancy between two
very different placenames.
I don't think this problem will just be confined to domainers,
who view the name, either. Most internet user's will know
this I think, and when they see it I don't believe they will
accept it warmly.
The only exception to this is using '.co' for what it is meant
to be used for, promoting company names.
In that scenario there is more of a synergy, i.e. business
name + .co. It is credible and makes sense. Geo + .co,
doesn't make much sense, unless it is a very high traffic
placename.
Costa-rica.co earns a further demerit because it is clear
that it's trying to get synergy with the suffix, and visually
it kind of achieves that, but in reality it is a bad domain.
And, of course, we've already mentioned the hyphen.
Good luck,