I was considering doing the same thing a couple of weeks back and decided the change wasn't worth it.

1. Hyphenated URLs do generally speaking just look nicer, but how likely is that to impact things like UX or CTR rates? (unlikely). It certainly doesn't impact rankings - just do some generic searches and you'll find a real mixed bag of hyphens and underscored URLs in the listings.

2. If your underscored URLs have been around for a long time then chances are you have some link equity built up into at least some of those URLs. 301 redirecting from underscored to hyphenated versions of the same content is an  unnecessary risk to some of that link equity.

If I had a relatively new site, low traffic from organic search and no real link equity then I probably would take the plunge and update from underscores to hyphens, but it would be an almost cosmetic move based on my own personal preferences. In your case I would advise against updating the URLs unless the domain has no pre-existing equity to give up.

Ben

Few ways to look at it I guess...

1. PageRank is a shaky metrics to use for analysis any way.

2. Its an easily achieved, followed link simply by shedding some cash.

3. Its $149 or $299 - how does that sit vs, your marketing/link acqusition budget as a total? what is normal cost per acquisition? I don't mean in terms of buying links directly, but producing  "stuff"  that helps you to acquire them.

In essence, can you acquire as good if not better links for a lot cheaper? If so....save your money, invest it elsewhere.

If budget existed for directory listings I would still pop myself in there personally.