I actively try and avoid buying records that are 'in demand' and so are also at their theoretical top price.
This means that if I didn't already know the record before its current phase of popularity I will just wait until the demand and price drop - which they very often do.
Most importantly (and this for me is one of the key aspects of successful of collecting) is the active researching and hunting down of good records that have not yet had their time (i.e. before they go big and go up in price) - but not everyone has the time or inclination to do the hard work with this.
Paying top price for 'in-demand' records, unless you are a DJ, seems like a waste of money to me.
Cheers
Richard