Here are three oiptions for investing in domain names:
1. Parking,
2. For Resale,
3. For developing into a Web-site.
Overture without extension basically means that the 3 word phrase is being searched for about x times, in your case 50, which is probably closer to 10-15.
1. This basically would mean that you are very unlikely on getting any revenues from parking the domain, through type-in traffic, and as well, since the domain is not developed than you will probably not get picked up by the search engines.
2. Based on the overture alone, it is very unlikely that the domain will have any high value, like over xx.
3. As I mentioned before, if your planning on developing a site, than it does have some value, since app. 500/month will be searching your search term, and if you develop a site well, you are likely to get in the top 10, which means that a good percent of those searchers will get to your site. Moreover, the fact that the 3-term expression has an ovt. of 50, there are probably other terms with much higher, which will allow you to develop those key-words as well. You should also research how much the ads are worth for those key word terms.