"Jay and Silent Bob Go Down Under" is mostly for Smith/Mewes fans as we see them chit chatting on stage in Sidney, Australia. No references to their previous movies whatsoever and just funny (depending if you like Jason style or not) stories about Jason (sex) adventures in Australia.
The only interesting bit was when Kevin revealed the true nature of why they are doing these tours, which is basically to help Jason stay clean of his drug addiction. This is always a subject worth expanding further.
All in all, if you like Kevin and Jason you are going to mildly enjoy this one, but in the end you need to consider that this appeal to how much you like them rather than offer any content that is worth it beyond that.
The only interesting bit was when Kevin revealed the true nature of why they are doing these tours, which is basically to help Jason stay clean of his drug addiction. This is always a subject worth expanding further.
All in all, if you like Kevin and Jason you are going to mildly enjoy this one, but in the end you need to consider that this appeal to how much you like them rather than offer any content that is worth it beyond that.