A trend we can see is that companies using MIFARE Classic solutions today are moving to MIFARE Plus without the "upgrade" to higher security levels. The reason for this is that the "MIFARE Classic encryption principle" in MIFARE Plus chip can not be hacked as easily as the old MIFARE Classic chip.
You simply get a more secure system with new MIFARE Plus chips, but the system in general does not need to be upgraded.
Please contact us if you are interested in a solution for your systems.