I would agree with that, especially as the paying client will deliver the xls as the requirements and expect something that looks similar. It takes a lot of work to refactor the process and then build and design something that's familiar enough to be accepted but different enough to be an improvement. Have had to do this kind of thing many times.

Where systems do win over spreadsheets is definitely in terms of data integrity, security and multi user experience so remember to sell the benefits and not just "look at the cool web experience / app we built".