More than one wife is a luxury I guess, if polygamy is allowed then women should be allowed more than one husband, this way diseases will be spread.
Due to my knowledge of Sikhism I reckon it's NOT allowed... it is too stressful to practice one life and as the Muslims say it is permissible if you can treat all your families equally... which will be practically impossible to divide your time equally between them all. Having more than one spouse has no purpose, if a man is not getting 'enough' sexual pleasure from his wife then he must sort himself out, it is HIS fault for being over-interested in sex and being too attached to sex. Thinking about sex too often is kaam, having sex more than about 4 days a week is probably kaam [this is my opinion].
Reference:: Sikh Philosophy Network http://www.sikhphilosophy.net/showthread.php?t=3777Reference:: Sikh Philosophy Network http://www.sikhphilosophy.net/showthread.php?t=3777
I would be surprised if polygamy is not mentioned in the Sikh scriptures somewhere.