Cricket shoes have evolved to the point where they are basically running shoes with spikes anyway; NB CK10 and Asics Gel Adv 6 being notable examples.
Gone are the days where a spiked up pair of trainers would be miles comfier and way lighter than the lead weights marketed as cricket shoes.
That being said, spiking trainers offers a much wider variety of styles and colours. For example I have spiked up a pair of blue/pink tennis shoes for T20 as we play in blue and pink kit.
If you are going to buy a decent pair of trainers and then spend the extra on spiking them up, you may as well get the best cricket shoes as you'll be spending similar money. Unless you really want a particular trainer or just find cricket shoes uncomfortable i think cricket shoes are superior. Spiking is a service we offer and whilst we do a lot of white (ish) trainers for 'proper' cricket, there is a definite trend towards jazzy coloured trainers for midweek/T20.