Do you guys think it will be worth it to skip current 1400 chaos dungeon and velganos to max our rested xp for 1415 chaos dungeon and deskaluda?
yes ofc
It depends on your goal. Is not more efficient in loot gains (mainly stones/Leapstones/shards) as you will net loss regarding that part of the loot tablr, but you have a low % chance of obtaining lvl 4 tripods on Chaos Dungeon and Relic accesories on Deskaluda.
Be mindful that there is just a low chance of getting a drop, and after that more RNG on the stat/quality/tripod/engraving, i.e. there is more chance of getting a not useful engraving than a ‘BiS’ one and even getting ‘BiS’ have another RNG aspect on the plus. As relic rolls go from 3-5 on the big one & 1-3 on the small one.
If for you its worth the gamble, go for it. If you are still pushing/in need of mats, don’t.
Deskaluda yes for the gamba, chaos dungeon not really but if you want extra gamba with gigalow odds sure go for it 
But statistically it’s not worth it since the droprate is super low for Deska as well. But as I said, it is worth if you want to gamble for a big relic day one, I’m doing it too
its the same question as do you gamble on accessories with your argos blood or do you dismantle them into great honor leapstones, the idea is the same, you sacrifice your gear progression for a chance to gamble at valueable drops
the only worthwhile rested could be the guardian, 1415 chaos is awful to gamble on and anyone who advocates for that has no clue about the average loot drops from there, saving for 1445 dungeon is only slightly more reasonable
Unless you are 1445 I personally wouldn’t. Keeping some tradable mats to sell after the patch will net you way more than some chaos dungeon gamble.