as always it depends on your priorities and your discretionary funds.
I have been using and upgrading my 08 trek and I'm done, looking to step up to a 6-8k bike.
Do I have to? no. My bike(s) is in perfect shape.
do i miss all the oos and ahs when you roll up with a new bike bling? yep.
will a new bike make me faster? mentally definitely, physically, minuscule.
If you are unhappy with your current bike and think a new one will make you ride more then get a new bike.
flip your old bikes for new or start a collection, just make sure you ride them.