One advantage some investors see in a low price to net asset value approach is that one need not have a really large portfolio, 25 or 30 assets for instance, and need not monitor it as closely as might be the case with individual stock securities. 5-10 are probably plenty if chosen well, and one can simply leave them alone for 3, 6, or even 12 months, then weed out those which have gone up enough, have sufficiently reduced discounts, and/or have been held for a couple years, replacing them at that time with new bargain CEFs.
Occasionally the market as a whole will be high enough that one cannot find qualifying CEFs. This is a danger signal, a good time to avoid new investments and instead to reduce holdings somewhat and increase reserves, for a significant market pullback may not be far behind.
Another technique that is useful may be to merely keep a good allocation in different asset classes, for instance a 5% investment in money market funds, 35% in global income funds, and only 60% at first invested in closed-end stock funds. Then if one's desired allocation gets skewed by more than 10% one way or another, sell shares in the class of assets which has too much and buy more of any which have too little, in order to bring the portfolio back into the desired alignment, in the process selling some shares higher and buying others lower. If for some reason when it is time to buy more stock funds using this method there are not enough qualifying CEFs, make up the difference for the time being with exchange traded funds (ETFs) (index funds that trade like stocks) rather than compromising one's CEF buy criteria.