Yep, At Jam is tempting. I wonder how the layout of the stages will turn out and if they are big enough. In that case VIP tickets wouldn't be necessarry if getting back and forth between stages will be easy. So far VIP tickets don't seem worth the price. I can get by without the centre area, especially if it is only limited to Strawberry stage. Those Meet&Greet Session should be something additional to the regular ones, I assume. So nice to have but not required. Further details are needed, especially regarding organisation issues.
Getting there really is restricted by the Keiyo Line. Or would the Sobu Line to Makuhari Hongo be a suitable option? 15 minute walk doesn't sound too bad.
So who is currently contemplating of going there?
About TIF:
Hot Stage should be in Zepp DiverCity again. Good choice.
My Navi Stage was further away, but it offered some shadow at certain times. I liked it. And I doubt the new Ship stage being that much closer.
Marketing Square is still not displayed. I wonder if TIF will really change it around, providing more sun shade and stuff for both idols and fans.
Of course Sky Stage still stands, with its crappy access.
I only noticed by your post that they got rid of Enjoy Stadium. Why? It was a good place too cool down.
In summary TIF has 6 stages now. In the light of the event going for 3 days this time it may be sufficient, if they don't get overboard with participating groups (probably will as they want to get over 200).