Well, I was watching the movie Elizabethtown (2005) and during the Orlando Bloom road trip scene near the end I heard a song that INSTANTLY reminded me of Ghostbusters:
What's interesting about this song is that it was released in 1967 (it peaked at #12 on the charts [source]), a full two years before the ET Mensah track. Even more interesting is that after the lyric sections, there's a break (or is it a "bridge" - I'm not fluent in music-terms) that is very reminiscent of those instrumental guitar sections in Ghostbusters. You know, those parts that sound like the Ecto-1 siren where Ray comes in and says stuff like "I ain't afraid of no ghost" and "Busting makes me feel good". (I have not yet heard the whole song, but I think the sample is a pretty good representation of the entire song - it's also roughly the same as the part of the song used in Elizabethtown.)
Since I had never heard Let It Out prior to watching Elizabethtown, and thus had no preconceived notions of the song sounding like Ghostbusters, I think I can safely say that I'm not trying to hear similarities were there aren't any. Feel free to download the sample, listen for yourself, and post your comments.
Now, as far as the Ghostbusters bassline and the whole Huey Lewis case, I've read in a few places that "Pop Muzik", by M (remix? sample), which came out in 1979 (a few years before Huey's song), is very similar to the shared beat. I've recently come to the conclusion that the bassline is even somewhat similar (though not 100% identical) as the beat in Roy Orbison's 1964 release "Oh, Pretty Woman" (if I'm crazy to think this, let me know).
With all of these songs released before Huey's "I Want A New Drug", I really wish the case went to court as I think it could have been argued in Ray's favor.
By the way, the ET Mensah song can be downloaded from AmazonMP3, but currently is it only available as part of a full album purchase. So unless you want the entire The Last King of Scotland soundtrack album, you're better off getting the full-length MP3 for free from Proton Charging.