It would be advantageous for your knowledge/career.
It may provide extra functionlity which could be advantageous to your company. You will need to research what extra functionality applies to your system.
Once you have eliminated all of the impossible,
whatever remains however improbable,
must be true.
If you have no desire to use the new functionality it is quite hard to justify from a developmental point of view. That said, once the new features are available you will more than likely start using them since some of them are very useful.
I've done many 7.3 -> 8i and a few 8i -> 9i migrations and I've rarely seen an performance increases. Typically, the kernel is a bit faster in the newer versions, but also a bit more resource hungry. The net result is approxiamtely the same performance.
I've only had one project that suffered significant performance problems as a result of migration. I'm still working on that one now The optimizers are quite different between versions and it seems to have an adverse affect on this project. In this case it's a very big, badly written web system. It's worth spending some time assessing the affect of the migration on your systems.
The administration and stability of 8i and 9i are significantly improved compared to 7.3. Initially your DBA will thank you more than your developers.
Make the move sooner rather than later. As the previous post suggested, support is a major factor.
You could move to 9i straight away, but it might be wise to wait until Release 2, due about May-ish. That's not to say there's anything wrong with the current version. I've had no problems so far.
Support is the major factor as Jeff said. Be sure that your DBA knows the newer version (8i or 9i). Some people run 8i or 9i using the features of Oracle 7 only which I find rediculuos. If the DBA, the organization is not familiar with the new version of Oracle you might run into trouble with ssomething at some point.