If money is no object, aluminum blocks are a nice way to save some weight. Most of the aluminum blocks are also more "high performance" than their iron block, garden variety cousins.
Case in point: an aluminum L33 out of some Silverado has flat top pistons, floating wrist pins with a larger bore, a slightly warmer cam with more duration, shorter head bolts (since the block structure was improved), and 799 heads (which are basically "Z06" heads). BUT, they are largely more expensive by 2x compared to an LM7 (which has dished pistons, 706 heads, etc).
I picked up an LM7 with 140k on it and everything still attached for $600; basically a take-out of a running motor. The nearest L33 I could find was $1,200 and had no accessories, no starter, and more miles. I used that saved cash to buy the cam, lifters, head gaskets, and head bolts.
Eventually, it will be force-fed, and likely rebuilt with larger bore pistons and other junk in the future, so the iron block is actually a desirable trait for me. But, if I was going to go with a sub-600hp, NA build... I would have spent the extra bucks for an aluminum block starting point.