I actually never found the time it took to cast buff spells as a huge problem. A slight annoyance, yes, but at the same time it was satisfying to know that it provided a just punishment for players who engaged in unrestrained rest spamming - which, lets face it, was a far too convenient cheese tactic in the IE games... )
What I did hate about buff spells though, especially in IWD2, was that some of the long-duration ones ('Stoneskin' and 'Armor', I think) covered characters with a monochrome gray color from head to toe. So if I cast those spells at the beginning of each day and once more when they ran out, the affected characters would look like walking gray statues during most of the game. Not good for immersion or identifying with your characters.