I spent a lot of money on building up my Amiga 1200 with all the bells and whistles (did it a few times) and for all you gain I personally don't think (now) it worth the hassle and expense.
I mostly used my Amiga for gaming and gfx work and it was nice to play games like hereticII, wipeout and nightlong but you can get all these games that run better on a pc for next to nothing. So once I sold my BPPC's I decided I needed my Amiga fix and my first thought was OS4 but the price yet again was something to think about.
But then a few people recommend MorphOS, so I looked into that and with MOS having a FAB hes sorted all my amiga needs and Morphos is a system you can use everyday. So Morphos on a mini mac was a perfect replacement for myself. so if you going to go NG then personally ask questions and more question,watch videos and see what system is for you!