That's a very useful tool! Currently, I use MSVC++ for .dat file editing along with coding, but this seems to have some advantages. Data verification would indeed be a good addition, as would the ability to search (and replace) and sort by different columns.
Edit: One bug that I have noticed, however, is that it does not correctly handle .dat files which specify more than one object, as is common in Pak128.Britain and legal as far as Makeobj is concerned: in those cases, it shows only the last object specified in the .dat file.