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.
It was a major political power not just in the region, but globally. Tito led and co-founded the Non-Aligned Movement, and effectively maintained sovereignty during the peak of the Cold War. It had a unique liberal flavor of socialism, where people enjoyed high standards of living, intellectual and cultural freedoms, freedom of movement (the Yugoslav passport was accepted globally), housing as a social right, decent wages, universal healthcare, etc. People were generally very happy. This is a big reason why "Yugonostalgia" still persists today.
Yes, the regime could be considered a dictatorship, with a strong police presence, and there are documented human rights violations, but it was far from an oppressive country.
Slovenia and Croatia were indeed wealthier than other regions, but the fiscal burden you mention is part of the socialist system that ensures a respectable standard of living for everyone. This doesn't work if there's a large wealth disparity between regions.
Yugoslavia was an interesting country with a unique political and social model which was not perfect, but IMO had less faults than the systems we have today. I think it's shortsighted to say that it would have the relevance of Bulgaria and Romania today.
I can bet a half case of Guinness what if you describe that to a modern American sans the mention of the country most whould confirm what this is what happening now.
Oh Hystory, YSOAB.