Upgrade guitar, or get a new mandolin (to learn)??

[Pen]

Get the nicer mando and keep the guitar.

My guess is if you like mando half as much as I'm guessing you will, you'll find yourself playing your guitar less and less over the next few years. You're Martin is a really nice instrument. That Collings (or a similar instrument) will keep you happy for quite a while.

When I bought my first Mando (after playing guitar for 8 years), I spent the lions share of my time playing and learning mando for the next 4 years or so. When I play for fun, it's back to about 50/50 now. Boy was I obsessed with mando once I got started.

I'll be there's plenty others on this board that can relate.