Magnus/Minnus have brushless motors, and the Magnus is considered a "flagship" scooter. Both of those features help with resale value.
Also, the Viper LiFe has a history of the battery not lasting as long (lifespan as well as burn time) as well as being slower than the Viper Lipo. The Viper Lipo is worth (to me, at least) a notable amount more than the Viper LiFe (almost 50% more range, faster, same size/weight, etc).
The Viper Lipo will get like 75% more run time than the Cuda400/Piranha P1 (360Wh). The Piranha P2 should give comparable to the Viper LiPo. The Viper LiFe should get nearly 50% longer run than the P1 or Cuda400.
The Magnus is notably faster than the Viper LiPo with a noticeably longer range (more than the 950/888Wh vs 777Wh would directly imply).
This is a notably Florida-centric viewpoint, but:
Over the last couple/few years, used DPV prices have taken a pretty noticeable dive. The UV18/26 that Johnny said are going for $700-$1000 today were going for $2k+ just a few years ago. A used Magnus was hard to find much under ~$5500, but can be had now for ~$4k. Vipers used to go for ~$3000/$3500 for LiFe/LiPo but are now going for $2000/$2500 or so (maybe $3k for a nice Viper LiPo). I think the biggest factors in impacting the price drops are the increase in competition in the DPV market especially in/near cave country. DiveX never penetrated Florida very much, nor did Genesis or Suex (Halcyon for a while). A few years ago, Bonex and Suex got a lot more support. It seems like they also updated models just prior to the increased US-based (and FL-friendly) support, which were very much welcomed after years of SS stagnation.