Is there any difference (advantages, disadvantages) between connecting my latest generation mac mini to my Pansonic HDTV using a Thunderbolt to HDMI adaptor vs. just using an HDMI connected directly from the mac mini to TV?
HDMI cables are far cheaper than Thunberbolt cables or adapters.
For video to your TV, there is no advantage to using the Thunderbolt port. HDMI is capable of carrying as much audio/video as your TV can display.
The advantage of using HDMI is you won't have to buy a thunderbolt/MDP to HDMI adapter. It's a simpler solution and there's no benefit to using the thunderbolt port with an adapter in this case.