20,000 SPG will get you 50,000 HH through AA. I think it will cost $25 to make the final transfer. Although I would prefer to have the SPG points, if you needed the HH points this is a way to get them.
Good point. I might put this to good use for a future stay in Tokyo.
Westin Tokyo (SPG Cat 5) = 12,000 SPG points per night during off-peak (16,000 if peak!!!)
Conrad Tokyo (HH Cat 6) = 40,000 HH points per night
Conrad Tokyo is, by general consensus in the Japan forum, a superior hotel to Westin Tokyo.
Need 5 nights, so I could convert 60,000 SPG points to 75,000 AA miles, which I could then convert to 150,000 HH points at a cost of $25 per transfer. Hilton offers to HH Amex card holders the AXON award (125,000 for 4 nights at Cat 5 or 6 properties). The fifth night will require an additional 40,000 points for a total of 165,000. Net additional cost to stay at the better hotel (Conrad) is 15,000 HH points plus $25
for the 5 nights. I think it's worth it.
A quick search thru SPG and HH websites reveals that a similar arbitrage opportunity exists in Hong Kong where Conrad HK is IMHO vastly superior to Sheraton HK & Towers.