With the small selection of adventures on offer, I think map frags have lost their value in terms of price/cost and usefulness. I think that section in the merchant needs an overhaul. Introduce more and harder to obtain adventures into the mix. We receive map frags from explorers and excelsior but are just stored and not really used.
If they were to introduce more adventures for map frags they could increase the price of said adventures so they could maintain some rarity. Thus giving map frags a new purpose while giving players more adventure options.