I don't understand why is it so important to have a 64bit PL/SQL Developer? 4Gigs of RAM isn't enough for your daily work, or something else? Because I do not see any reason for such a software (web browser, mail client, office, pl/sql developer, etc) to be a native 64bit application. Video editing, and some very special tasks, where a 4GB memory is a limit, and using 8-16Gb could be much faster, but otherwise, it is not important.
On the other hand, it is better, if the application is a 32bit app, and it means, that memory leaks, flash player, or javascript errors cannot kill the whole machine. I had such memory problems with some websites, and with many opened tabs, and Firefox startet to allocate 3Gigs of memory, it died later, but my PC with 8Gigs of RAM didn't noticed anything. If it were a 64bit app, it could use all the 8Gig memory, making the whole PC unusable. (As it was with Chrome, because chrome launches all browser tabs in a separate process, and this 4Gig limit applies by process).