Since my previous reply seems to have been purged, here goes another try...
TL;DR - Not worth it without serious fixes.
I've tried three of the Weekly Challenges so I could say I knew what I was talking about, and for two reasons I come down firmly on the side of Not Worth It. The Challenges are far too 'all or nothing' to be worth the required investment.
Reason 1 - The Adventure side of things is simply broken. For the vast majority of players the Challenges require Adventures/Scenarios that are rare or essentially unavailable without dedicating an unreasonable amount of time and resources. Especially given the Dev Notes, this seems intentional, so that points to either poor or malicious game design.
Solution 1 - as suggested by many, simply expanding the selection of Adventures/Scenarios to include all of a given category (Ali Babas/Co-ops/Scenarios/etc) would go a long way to balancing the 'fun' with the 'challenge', because currently the Challenges are none of the former and an unreasonable amount of the latter.
Reason 2 - Purging 2561 Troops per cycle of four Challenges. This unreasonably ties up our Troop production during the same time we need those buildings to make Troops to complete the Adventures required for the Challenge.
Solution 2 - Add in an additional Adventure that uses the Troops representing the Resources BB wants us to burn. At least that way we get something (XP and Loot) for the headache. I'd rather run an extra VLT or YWC than purge 2561 Troops.
Bonus fix - make the Search requirement "X Search *or longer*". All my Explorers are always out on Prolonged. Unfortunate timing means I could be waiting a day or more to turn them around onto something shorter.
Global solution - scale the Token Rewards so you get a small amount for each stage of the Challenge, with a bonus at the end. That way players who can't get the required Adventures/Scenarios can still participate but those who do the whole thing are rewarded for their efforts. Some participation encourages more participation down the road, while shutting players out entirely just creates annoyance and frustration which creates bitterness that leads to less participation in the future.
...but that's just basic game design.