Assuming they are general circulated coins, not a great deal. Yes one of the two types is scarcer than the other, but collectors of decimal coins are usually only interested in high grade coins or varieties. In many cases, they won't even be aware that there are two varieties for this date/denomination. Plus, of course collectors of decimal are not usually expecting to pay big money for their coins, since most can be obtained from change as they are issued. My guess is maybe £5 the pair, if somebody out there wants the scarcer type.