Difference between 3/8" ID and 1/2" ID in reality to the enduser is next to bugger all - for most it's unnoticeable. Know plenty who have moved from 3/8 to 1/2 and vice versa who have noticed no change whatsoever.

Note - the 3/8" tubing that supports compression fittings tends to be 3/8" OD (8mm ID 10mm OD) and is generally fairly prone to kinking due to the 1mm wall thickness... unless you've managed to find some 3/8" ID 5/8" OD compression fittings to allow you to use the common Tygon or Clearflex 3/8" ID hose that most places sell... which leads on to...

Note2 - OD of 3/8" tygon / clearflex and 7/16" Masterkleer is the same for reference... so if using 5/8" OD compression fittings on 3/8", the space consumed on the block / closeness of fittings is irrelevant as the tubing OD is the same.