Don't let anyone judge you for spending or not spending your money. Everyone is welcome to play as they like.
But there are things that I would take into account even from my short-term perspective: Season 1 is simple anyway if you put some dedication to the game. But there seems to be not much "give a strong start" for more than one season, since no matter how strong you are now, you'll be matched with a similar opponents next season.
When you spend, get ready to be facing stronger opponents who are also willing to pay, and may be more than you do.

My personal example:

(1) I have a main team, spent around 9$ for special sponsors on level 2 and 3 and not sure if that was a good idea.
Season 1: Won a league (joined too late to participate in the Cup), finished at ~95-98%,
Season 2: Bought a special sponsor, got quadruple there with 0 losses for the whole season, finished at 105%. The league was an easy walk. Tried to get rid of too heavy players in the end of the season, dropped to 100%, but still...
Season 3: Started with 80% in a league with almost all ~80-90% teams + one guy that bought a fresh 115% team (on day 2 he had a bunch of 116% scout players + 2-3 140%+ players, all fresh with 0 games played)... Currently I'm #2 in my league with 2 losses and you can guess who is #1.
Won the cup, but got smashed in CL by a +10% stronger opponent (and all the CL semi-finalists were +10-15%). Currently at 113% and plan to get rid of 7-9* players I got from special sponsor and the last event since they are too old and heavy for the next season.
Overall stats: 106 wins, 6 draws, 3 losses, 501 goals scored, 62 against.

(2) alternatively, my wife's account that I'm also playing since season 1. 0$ and much less time spent. Twice less watching ads, no market hunting.
Season 1: Joined at mid-season, still won the league. Finished at 95%, was stronger than the main team.
Season 2: League was an easy walk, won the cup, got trolled in the CL final against a weaker opponent. Finished around 95%.
Season 3: League was an easy walk, won the cup, got beaten in CL by a stronger team in a draw with extra time. Currently at 100%.
Overall stats: 107 wins, 4 draws, 1 loss (damn that CL final), 550 goals scored, 45 against.