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Although the turret charactoristics did have much to do with the baselength, even in WW2 the longer baselength of the turret RFs was considered important, not just a useful by product. The Repulse survived its weight sensitive refit in the 1930's with three 30ft RFs and three 15ft RFs, two of 30fts being left on the turrets. The 30ft on A turret was additional to the normal 15ft and could easily have been removed if the 15ft was regarded as sufficient. Similarly on the Renown the RN took the trouble to swap the Y turret 30ft with the B turret 15ft after the main refit. I'm unsure why they did this - the best reason I can think of is that the Y turret was very low down on the R&R's and probably subject to spray as well. The fact that they carried out this work during war time indicates that they considered the long base ones important.
The long base turret RF also played an important part in rearwards FC. AFAIK the only BBs in the RN that had the same non turret capability at the back as the front were the Nelsons and the Vanguard. With the others the non turret RFs seem to be smaller or non existant. I believe many other navies also followed this trend.
With Nelsons of course there were no other rear mounted long base RFs so I suspect this is why it bucked the RN trend. The Vanguard by then veered towards the later US style.