Found a wonderful replacement for importing Yahoo Finance data into Excel via the old now-broken macro from Gummy - smfGetYahooPortfolioView, an Excel add-in:
Took me a while to figure out how to make it work, but after a couple days I had it fixed and automated - and it gives BVs plus allows you to calculate values for CEF premium/discount via NAV symbols, like xPDIx.
As far as "historical and numerical evidence of the wisdom" for buying CEFs at certain discounts or premiums, don't think I have to write that up myself, there's plenty out there about this - generally, I won't even look at a CEF trading at more than a slight premium, and if one the historically trades at a high premium drops into my range (+5% or less) because of general market dysfunction, not anything fundamentally wrong with the fund, I'll consider buying it. Recently, the once high flying PHK (35% to 50% 3 yr premium) dropped below +10% premium, making it a buy for some folks, but it cut it's div the two times in the last 1 1/2 yrs in Jan 2017 - that drop to +8% premium did *not* make it a buy in my eyes, just reflected the increased risk of their portfolio. As far as discounts go, sometimes they're just in out of favor sectors - if the div is steady and being earned, and their DRIP gives you a typical 5% discount to MP or new shares at NAV, to me that's like free money - no problem, and actually a reason to buy - I'm getting $1.05 for each $1 of divs paid.