In my opinion it's worth it. I have been paying the $30 since June of this year (albeit, back then it was not capped at 5gb, but was unlimited on up to 8 devices), and have enjoyed using it very much.
I also own the WiFi Tab 10.1, and when I want/need connectivity it's nice to know that I have access anytime/anywhere.
My previous phone was the Evo 4G, and the hotspot would kill the battery in about an hour or so of use, but the Epic Touch has good battery life even with the hotspot feature turned on.
NOTE: The fee is month to month so you don't have to sign a contract (YAY!!). The only thing I don't like about it is you have to call Sprint (one time) to turn it on initially, and you'll have to contact them again if you decide you no longer need it.