WIth any domain suffix if you are able to develop it with the right content that will get it listed higher in Google and other search engines then .to could well be worthwhile. What you would lack is the number of internet users who automatically type in 'domainname.com' (and to a much lesser extent .net/.info/.org).
Of course availability of a more prominent suffix plays a great deal on whether the .to suffix is worth developing. It may well be that more popular suffixes are not available to register or purchase on the aftermarket or if available is prohibitively expensive, then this would make a lesser known suffix more attractive to develop. (Here also should be considered that the domain and suffix may result in an HDN - 'Hacked Domain Name' - where marketing and memorability could be a plus for a lesser known domain suffix, examples could be 'want.to', 'get.to', 'sell.to', 'shin.to', 'in.to', etc.)
Parking such domains is though generally less rewarding unless the domain has been previously a site and has residual existing traffic.
N.B. I have noted that it appears a lot of the developed sites on the .to suffix are in Japanese, so if parking it may well be that the base language selected should be Japanese to try and maximise returns.
Hope this helps, but whatever you decide to do good luck to you.