Talk to your guidance counselor to see if non-diploma students are still listed as “most rigorous curriculum available” students on the GC’s form for college applications. It usually depends on the school and on what else the students is doing instead of the full diploma requirements. For instance, at our school, some of the super STEM-y research kids were not full diploma kids because they were taking a college science or math course in our town rather than taking IB BIO HL or Math HL. Those kids were still considered “most rigorous curriculum” kids. Other kids who chose not to do the full diploma for reasons such as timing and schedules, were not “most rigorous curriculum” kids.
My diploma kid’s application experience suggested that being a diploma candidate carried a lot of weight, and many of his interviews involved talking about his EE, TOK etc.