I am not sure what interest it makes to collect stamp sheet. Reason for this is it will required special care for sheet you collect and it will not fit in any standard philatelic album and it also cost higher than regular stamps.
Seller : estafette50
Buyer : traditional.india
Sold for 32 Euros in auction.!!
In future you might see this stamp sheet selling on ebay or delcampe in block of 4!!
This is for reference for future new Gandhi Stamp Collectors, so they know what was pricing of this stamps in 2011 even after 40+ years!!
This 2 sheet came for sale for $500!!! But both of them were unsold. (Looks like one of the buyer is trying to sell this.!!)