Hi Keith,
Good question!
The I-VI-II-V is great because it’s a cycle. As you point out this makes it a very free and fun progression to improvise over.
A variation is to reorder the the chords starting with the II chord, so it would be II-V-I-VI.
Even though you are playing the exact same chords, you will find that your improvised lines will take different shapes and contours.
Perhaps try a pattern in minor tonality…
Here’s another 4 bar repeating pattern or cycle that works in minor keys:
II-7b5 / V7alt / I- I-maj7 / I-7 I-6 / then back to II-7b5 to start again.
It’s basically a minor 251, and the last 2 bars you are adding a minor line cliche.
In G Minor, you would have:
A-7b5 / D7alt / G- G-maj7 / G-7 G-6 /
This can be nice to play around with the modes of the melodic minor.
Over A-7b5, you can play the Locrian natural 2
Over D7alt you can play D altered mode, or D HW Dim
You can also play the G Harmonic Minor Scale over both the A-7b5 and D7alt which is a cool sound. Angular sounding, but nice! Try to outline the characteristic tones from the underlying harmony…
G Harmonic Minor contains: G-A-Bb-C-D-Eb-F#
- Over the A-7b5, the Eb-D-C work well
- Over D7b9, the A-G-F#-Eb-D-C all sound great to my ears
- Over G- in the last 2 bars it’s nice to outline the G- triad with the 9 and major 7th
Finally with the 2 bars of G Minor, play around with the G Jazz Minor Scale, also known as G Melodic Minor (G Dorian with the major 7th, or G Major with a b3… however you want to look at it .) The characteristic note of the mode is the major 7th, so try to accentuate that colour in your lines.
I jotted down some common progressions that can be used for vamps, I’ll dig out the sheet and post it in this thread 
Glad to hear your making progress Keith. We’ll explore more functional harmony in upcoming lessons… it’s the kind of stuff I like to explore in my own time!
Cheers.