If the goal is to get *any* upgrade you are correct.
If the goal is to get upgraded to a suite, I believe that your odds are definitely improved if you have booked a higher room type.
After a gazillion years (at least that's what it says on my dashboard

of travel, at this point special rooms are important to us.
We feel as if we have earned it.
Originally Posted by
kaizen7
I think SPG give more benefit towards Plats/Golds that book cheapest room than those who book higher category room.
for example
Room available :
Deluxe Room (112)
Premier room (72)
Executive club room (83)*
Junior suites (2)*
Executive Suite (11)*
*Club access included for these rooms
Case 1 :
A platinum member book 1 deluxe room for 3 nights
His chance to get upgrade is quite high as he have 168 rooms above his booked category that have the possibility to become his upgrade.
And even if he somehow very unlucky and the hotel is full, he still have benefit of club access.
Case 2
Another platinum member book a Junior suite, his upgrade chance is only from the 11 executive suites.
And also if he didn't get an upgrade, his plat club access benefit is not giving him any benefit as the club access already included in his room rate.