Is that you DW writing in?
I must confess Matchbox and I have had a 60+ year relationship.
However to spend this much money I think we are talking 1/43 scale or bigger collectors models.
Any collecting hobby can develop into something bigger than we intend or can honestly justify, something addictive.
I have my notional limits. No silly eBay purchases, no mail order from the US (postage costs more than the car) When our children were younger I had pocket money, a roughly set sum per week.
Are they worth anything - those sold as investments less so - because so many bought them at the time. You try selling Models of Yesteryear or Lledo models nowadays. All sold with an implied future increase in value.
I get them because I like them. Some of mine are worth a bob or two - but this isn't predictable, and it's only a few. Some because of rarity value - because few were made, because they were fragile and an intact unbroken model is rare or some were unpopular at the time. (Matchbox Ford Fiesta in red, 60s Harley Davidson with intact handlebars, 1060sLambretta scooter + sidecar respectively.)
My late BIL collected - but in different league to me. £60-80 each. He was addicted and spent more than he could afford although some of this didn't become clear until after his death. He bought anything and everything.
His are now in the process of being sold by a specialist auction house. So some of the money spent is coming back to my DS. Hard to say if they are being sold at a lot or profit.
Like all collecting - buy what you like, like what you buy.
So to the OP - I think you need to set limits, money, space etc. May be suggest other model car related outlets - making/converting them, trading them properly?
Must finish - off to B&M and Poundland to see what's new there!