We seem to have a good difference of thought on the worth of iWorks 09.
If you are comparing it to the 1990-1995 era versions, yes that was not real useful. When I use the 2009 version, it does everything I need and makes it quite a bit simpler to use. I have moved more of my things over to the iWorks 09 applications.
There are still some applications that I use Excel for. These are mostly the things I put together back 10 years or so ago and I am comfortable with them but if I had to write them new today, and I didn't have to share all of their features with other users, they would be done in iWorks 09.
If you write them in Numbers (or Pages or Keynote) you can save them in Excel (or many other) formats but some of the features will not pass through to the other formats.
Now if you are talking about Enterprise type applications, then I would suggest a stronger program. I don't know how many firearms you may want to inventory but, unless you are a dealer and have the large volume and detailed record keeping needs of a dealer, Numbers would probably do the job.