lucy24 - 4:17 pm on May 6, 2013 (gmt 0)
or Is it wise to send the old
(www.example.com/make_sense.php)urls to 404 error page by simply rewriting it www.example.com/make-sense.php
The question doesn't, er, ahem, make sense. Rewriting an old URL to a new path wouldn't result in a 404 unless the new location doesn't really exist-- and if so, why are you rewriting to it?
I suspect that when you say "rewrite" you really mean something else. But I'm not sure what.
Frankly I think lowlines vs. hyphens fall into "If it ain't broke, don't fix it" territory. Use hyphens in future URLs for new pages, but don't bother changing things that already exist.