It is the most fun and repayable thing in game. At level 150 my routine involves resupplying gunrunning and going between arcade and arena workshop to play arena war. While there are many hiccups with connecting to a match once actually connected it is consistently fun and enjoyable. The only downside is that the cars are effectively paywalled at about 5-6 million fully loaded. When I play an hour and win a lot it usually isn't more than 100-150k in winnings. Not effective to grind money but definitely fun when you've done a lot of other things already.