Mac Mini question
Do both. I have a new Mac Mini 2.3 i7 quad core 4G and 1TB HDD. But, I also have a 2012 MBA 13"(dual core i5) and have 8G RAM and the 256G SSD. That thing blazes past the newer and "more powerful" mini. I chalk it up to twice the RAM and the SSD drive. That SSD I really think is the killer feature. For now, I plan on upgrading my RAM to the max if 16G RAM (8+8) for $176 from macsales.com (OWC). Later, I'll do the SSD as the OS drive and the drive for intensive apps (ex. Aperture) and keep the 1TB drive as storage for lower intensity apps and storage.
Do the RAM first, it's fast and cheap comparitvely. If that doesnt do it, the SSD should.
After memory upgrade and SSD install,
Get your photos off the USB drive and move them either internally or onto an external firewire disk; much quicker!