Analog Upgrade Suggestions Welcome

I am thinking of making several upgrades to my current analog rig.

Current system: click here

First, I am thinking of upgrading my VPI HW19 MKIII to the MKIV. I would like those with first hand experience to tell me if the upgrade is worth the money, and what I can expect to hear in improvement. I am currently using the SDS and SAMA modifications.

Second, I am thinking of upgrading my cartridge. My Sumiko Talisman Alchemist IIb is almost 15 years old and is ready for retirement. Some A'goNers have recommended the Shelter 501. I didn't want to spend more than $1000 for a cartidge as the majority of my listening is still redbook CD. I am open to other suggestions. I want the best cartridge for the money. Also, I am leary of buying such a fragile item used. I have heard others on A'goN say they'd never buy a used cartridge. Please share any experiences out there; good or bad.

My current cartridge has an output of 2.0mV which I assume means high output. Will I need a step-up transformer for a low output cartridge? Is the Shelter 501 at 0.4 mV considered low output? My Classe Six preamp has a phono section. The preamp comes with resistors that the user can change out to match the volume control knob position to the level of line components. I assume I'd need to change the resistor I'm using with my current cartridge. Otherwise I'd have to turn the knob way up to get enough gain with a cartridge with an output that's 1/5 that of my current cartridge. Is that correct?

Thank you all for your help and suggestions.

Cheers!

Mark