that is a good deal for the W+ mod.
i can't answer whether or not its overkill for your needs. you can use other usb devices that are cheaper, but may not be the sound you want. the warm mod as the name implies adds warmth in the pre stage and is much cleaner than the stock ua-5, its a very nice sounding pre/ADC. i am not familiar with the mics you mentioned above so i don't know if they will compliment eachother.
if you can afford to spend the $500 for the w+ ua-5, i don't think you would be unhappy at all, its a great device and probably one of the better values for a pre/ADC box in this hobby. i believe these units sold upwards of 600/650 new, but i could be wrong.
there are tons of shows on archive.org using the w+ ua-5, i suggest you check some out and see what you think before you purchase.