Totally man, good post, I'm really in a similar boat. Odd times are an experienced thing, most people I talk to who are capable with odd time signatures just kind of shrug and say "you get used to it." I think when you're in music school these days you're forced to play in unusual meters all the time and you do just pick it up.
But for those of us who don't have that exposure we have to get creative and/or technical about how to handle odd meters when they come up.
Earlier this year I couldn't even take a non-stupid-sounding solo in 7/4 without losing my place horribly, but I've been working on it, and one of things I've done is pretty much exactly what your bass playing friend advised. That groove really makes things simpler...a lot of people play in 7, and sure people do it different ways, but half, half, dotted Q, dotted Q is by far the most common groove. Similarly, dotted Q, dotted Q, Q, Q, seems to be by far the most common groove in 5.
One of the things I've done related to that that I've found really helpful is to try to make melodies of standards fit into that groove. I took a list of about twenty standards that I was most familiar with and tried to make the melody fit into that rhythmic framework. Playing the
melodies with the groove really opened up my soloing.
A neat thing I found while doing that is that the groove is much more familiar uptempo than slow or even medium, but it can still work slow. In that process I worked on "Autumn in New York" and liked the results, so I made a little arrangement:
Autumn in New York - YouTube
I screw up a bit here and there, but they, that's the learning process for ya. I was trying to be somewhat loose and floaty for some of it but still keep my place and be locked in mentally.
One other thing that I think is really great...while you're doing all this stuff, trying to make those bass lines groove, set the metronome for half notes instead of quarter notes, so it clicks either like:
1 2
3 4
5 6
7 | 1
2 3
4 5
6 7
or
1
2 3
4 5
6 7 |
1 2
3 4
5 6
7
Good topic...