It would depend on the usage of your current system and the feature licences on the 3PAR system.
If running multiple tiers these two features can help;
Adaptive Flash Cache - Uses some of the flash space as a read cache for data on slower disks.
Adaptive Optimization - Moves active sub volume data up to faster disk (read/write) and non-active sub volume data down to slower disk.
If you have a lot of non-active volumes or data on volumes then that could rest on the NL drives, freeing up space on faster drives. Depends how stable your usage is, if it suddenly gets very active then it would be slow until the policy you set has a chance to notice it and move it up a tier.
Stuff you know is active can be either left on SSD or via another policy migrate between 10k/SSD depending on access.
I don't know what the reporting tools are like on EVA but you maybe able to get an idea of how much volumes at least are active.
I've run NL and 15k on a 3PAR before but we couldn't afford the features at the time to do the tiering. Since then all are arrays have only had single tiers (either 15k or SSD) so not had a chance to do this in practice (now that the features are inclusive
.
As to adding the 16Gb FC cards, yes they should work fine on 8Gb switches and you might get better performance from the SSDs with the faster cards/asics. Only issue I see on the 7000 series is that the 8Gb cards have 4 ports but the 16Gb cards only have 2 ports (the 7000/8000 series arrays have limited card slots for expansion).
Now that 64Gb FC switches are out you may find good deals on 16Gb ones to upgrade in the future.
Make sure to read the 3PAR Concepts and best practice guides, a lot of the array management side is automatic so you have to be careful not to bring too many manual practices from other systems as they can hamper the 3PAR arrays ability to give the most optimised performance.