The EEC is summed up by an old joke:
German: Is the EEC working?
Frenchman: Where are the panzers?
German: Still in their laagers, why?
Frenchman: Then the EEC is working.
If someone changes the language of the treaty of Rome to not include the phrase "ever-closer union", then there will be a de jure justification to not progress with currency union, tax harmonization, and legal unification.
However, it will still be in the interests of the bureaucrats in Brussels (as in any bureaucracy) to extend the scope over which their institutions have authority, so that their organization will need to increase in headcount creating more management positions for them to be promoted into.
It's probably impossible to maintain a balance though - if there are pan-European institutions that oversee any aspect of the EEC's remit, they will likely continue to slowly expand their areas of competence until there is either a federal European state, or nations withdraw from the treaty of Rome.