This is one of those things that's hard to quantify. In my estimation, changing the look and feel of the menus so that they are just like the rest of OS X won't make a bit of functional difference. You won't be able to do anything with the new menus that you couldn't already do with the old menus. So is it a waste of time?
This is the hard to quantify part. I was initially put off by the non-standard menus. I thought they were ugly and looked "wrong", and certainly behaved "wrong" (they don't stay fixed in one place; rather they move slightly based on where you click). It was one of several reasons that I did NOT want to LIKE MC. But the more I used, the more I liked it. It took me a while: 30 days trial, plus an extension. Now I'm a very enthusiastic fan of MC on the Mac.
That initial impression is important. I think the mental attitude of potential customers would be better if they saw more native looking and feeling menus. Instead of an automatic negative reaction (huh? What's up with these weird menus? Did the guys that wrote this even understand Macs? Maybe I shouldn't be using this...), you'd get the familiar mental reaction of "It looks just like I expect it to".
I'm not sure if this is making sense or not. More importantly, I don't know what kind of engineering effort this would require. Would it help first impressions? Undoubtedly YES. Help convert those demoing MC for Mac to paying customers? Probably yes. Improve actual functionality? I don't think so.
So is it worth doing? Hard to say. I lean towards YES, but again, I don't know the time, effort, and money side of making this change.
Just my opinion.
Brian.