yes, you can ignore the pool store advice - as long as you do not have any plaster or grout or mortar that is in constant contact with the pool water - low calcium in a vinyl liner is not an issue - in fact I try to keep my CSI (calcium saturation index - calculated by Pool Math) slightly negative which means that the water has a slight tendency to dissolve calcium - that way, I am confident I will not have any scaling anywhere in the entire system - if you play with the temperature in Pool Math, you will see that as temperature increases, the CSI also increases, and the water has more of a tendency to deposit calcium (scale) - so in my mind, that means the water always has a bit more tendency to deposit calcium in the heater - so to help ensure that does not happen, I figure keep the CH low and keep CSI low - then scaling is never an issue
Kiss4aFrog's comments about the concrete apron are reasonable, but I think the chances of that being an issue are slim
the only time calcium matters is if you have a plaster pool, an area that is tiled or other feature that includes mortar - in those cases you do not want your CH low and you CSI negative, or the pool water will slowly eat away at the plaster/grout/mortar - I think I recall a thread on here before about someone with a water feature (waterfall maybe?) that was made of rocks with mortar between them, and the mortar was being damaged by a lo CSI even though he had a vinyl liner - so if you have any of those things, then listen to them - otherwise, don't worry