If Yugoslavia had survived it'd have the relevance of maybe a combined Bulgaria and Romania today.

Slovenia and Croatia were the most developed parts of it and would be burdened by fiscal transfers to undeveloped regions of Bosnia Macedonia and Kosovo. I'd argue Croats and Slovenians enjoy a higher quality of living with a government that can focus on the needs of its own citizens.

You don't need political relevance or even resources to develop a great country. Look at Denmark as an example.