You might want to check this. There's another thread out there that suggests that park hoppers can only be used to upgrade to tickets of like kind. In other words, since the old park hoppers have both hopping and never expire features, they may only be used to purchase MYW passes that have hopping and never expire. (This seems different from what we were originally told, but another poster says she tried recently to trade in old hoppers for MYM and was told exactly this.)
A 5-day MYW with hopping and no expire is closer to $280, so it might be more cost effective either (1) to keep the 4 day hoppers and buy a one day ticket for the fifth day, or (2) trade in the 4 day hoppers on some longer term no expire hopper MYW tickets. Option 2 only works if you plan to return. (For example, you could use the value of your 4 day hoppers to purchase 7-day magic your way tickets with no expire and hopping. These cost about $310, so for an extra $30 over the cost of the 5-day MYW never expire hoppers, you get two extra days that never expire -- a value of nearly $200.)