Spikes are like redeco toys... they are there for the retailers to buy something "new", but can still be similar enough to the cartoon characters to still sell.
Retailers just want new/different product on their shelves as often as possible, so if a cartoon goes for more than a year, the character toys have to have something changed on them (colours, a new gimmick, moulding, new toy, etc)... and it is up to the cartoon to reflect those changes if they can afford it (CGI) or can make sense of it (standard animation) - like Transmetals, or Energon Powerlinx upgrades, or Movie mechtech weapons.
Maybe before the end we might see one or two have an upgrade, but being a CGI cartoon, the chances are slim, especially getting close to the end of the series (they won't want to waste time and money redesigning/resculpting CGI models if it won't be used much). They'd much rather spend the money creating a new character model, than reworking an existing one.