It is too bad that so many people are trying to manipulate the system and BGA seems to be trying to fix the hacks instead of improving the system. Spades has a high element of chance with incomplete information. ELO only works well in this case with a large number of games where the element of chance should be reduced by the law of averages. I would say that the biggest factor to improve the system would be to minimize that disparity in ELO at tables and discount unlikely results which are probably a result of the dealer or poor play from a lower ranked partner.
The way the system works once you have achieved a ranking you are happy with which is probably statistically unlikely, you should stop playing which means there are fewer players with higher ELO playing which makes it more difficult for people to catch up.
The idea of reducing points for the same partner was an attempt to make it difficult for people hacking the system by red-thumbing and always playing with their own dummy accounts to game the system. ELO decay seems to be counter productive. People play games to increase their ELO and then it gets disounted at the end of an arena season for not playing arena when the biggest reason people's ELO doesn't increase over time is being force to qualify for top leagues against lower ranked players.
I am suspicous of anyone who wins over 80% of their games in Spades. Unless BGA is pairing novice players against expert players I find it to be an unlikely occurrence. I think the idea of the rule is to penalize people who game the system by red-thumbing other playerrs, or use dummy accounts to cheat. Trying to create a system that doesn't favour people who play huge numbers of games when the ranking mechanism is inherently flawed and requires large samples is a problem. The large K factor for new players just makes the rankings more volatile and less reliable. Ideally BGA uses ELO to create groups of comparable ability and also uses the ELO to discount the penalty for higher ranked players so they aren't penalized for being social would be a good start. One easy solution might be to let people filter Arena games by ELO so you avoid the problem of different skill levels.