A coworker showed me this adapter available at Amazon (and other places). It can hold two Micro SD cards, and 'fuses' them into one for your MSPD needs. About half of the customer reviewers purchased it for their PSPs, and about the only negative thing they've mentioned is that the product is kinda flimsy.
In theory, you could get 32GB MSPD for less than the cost of a 16GB MSPD, since you can purchase 16GB Micro SD cards for much less than a 16GB MSPD.
The product itself is only about $15
http://www.amazon.com/PhotoFast-Mic...croSDH/dp/B001I0T92Q/ref=cm_cr_pr_product_top
In theory, you could get 32GB MSPD for less than the cost of a 16GB MSPD, since you can purchase 16GB Micro SD cards for much less than a 16GB MSPD.
The product itself is only about $15
http://www.amazon.com/PhotoFast-Mic...croSDH/dp/B001I0T92Q/ref=cm_cr_pr_product_top