How do you spend your Chaos Dwarf RARE points?

I'm similar, 2-3 in a standard list.

I have fielded 'pure' Chaos Dwarf armies though without hobgoblins though.

In those I always use a unit of 3 Bull Centaurs which act as the equivalent of chaff though.

As I play with mates using an expanded Chaos Dwarf list I usually take at least 1 golem (50 points) if I'm going no Hobgoblins.

I wish the siege giant had some other perks over the normal giant to make it more worthwhile. That armor save is barely worth it as people would want to use Strength 6 attacks against it anyway.

Glad to read he did well in the battles he's named for 😀

I think the model is pretty cool.

I never play at such a low points level, but I have fielded a pair of Destroyers in a 3000 point army.  So sort of! 

That's fair, how does double destroyer work out? Does it limit the rest of the army?

Personally I'm a huge fan of Destroyers.  Nothing in the CD army comes even close to matching its close combat prowess.  Infernal Guard make decent anvils, but are too slow and only have a single attack.  Fireborn don't have the strength to take on elite armour or toughness.  The Iron Daemon is too reliant on its charge against anything that is not thunderstompable.  Bull Centaurs have too few attacks, they are really missing that third attack per model.  Destroyers on the other hand have extremely potent offensive and defensive capabilities, while striding across the field with an impressive movement of 9.  Keep them away from the few things in the game that can counter them, and they will devastate everything in their path.  We put the Destroyer in a close combat math-hammer tournament against the very best non-character units in the game and it performed amazingly:  www.lustria-online.com/threads/the-best-close-combat-units-in-all-of-warhammer.25298/

As for fielding a pair of them in 3,000 point army, they pose a huge threat to the enemy.  Plus, you're still left with 2,350 points, which is more than sufficient to fill out the rest of the army around them.  There is still plenty of points left to field your lvl 4 general, war machines, core infantry blocks, BSB and some other elements.  In my opinion it is important that some of these points be dedicated to winning the chaff war (via chaff and/or anti-chaff units) to help clear the way for the Destroyers.