Pretty much you have been given all the appropriate advice.
Don't get into the ground level of motorsports shooting hoping to make any real money at it for several years, if not decades. Think about it in the same way as all those drivers starting at the club level with dreams of becoming a professional race driver. The majority of those guys racing at the local level lose money and never make the "big time". It's the same with motorsports photography.
Find a local track and get out there and shoot, in all kinds of weather. Build your skills. Meet people. Remember, though, when you are just starting out you won't have access to all the "good" parts of the track. You will be stuck shooting from the spectator areas which are notorious for not being the greatest places to shoot from. Track management and race/track day organizers aren't just going to grant anyone access to the track. Also remember that you are now competing with those guys who have been doing it for years, and have the connections with the tracks and organizers. You are going to have to produce a product that is at least equal (from worse shooting areas) to, if not better than, what those guys are producing.
Just like with racing, you need to put in your dues at the local level in order to gain access the the national level. And as was pointed out, most national level races will require something more than just "I am a motorsport photographer" to gain access to their events. You will need "sponsorship" (credentials) from someone, whether it be media or team. And then, at the national level, the number of photographers allowed becomes smaller. And then it get's tougher if you want to go international.
Also, as was pointed out, getting paid by the media is a rapidly decreasing opportunity. This is a growing trend among all photojournalists, not just motorsports. Organizations are less and less likely to pay for pictures (especially with the flood of people who are willing to give them away). I have been approached several times by publications that wanted to use my pictures. Until, that is, I brought up the question of what their budget was. Each time I got the standard response: "Well, we we're gonna make sure to give you credit." Sorry but "credit" doesn't pay the bills.
So here's the reality, most new bands want to be rock stars, but the majority end up playing the local bar scene. Same goes for motorsports photographers. Are you willing to put in the long hard work, lose money and time, and maybe a decade down the road find yourself making a living off it? Are you willing to haul yourself out of bed early in the morning to make it to the track for the driver's/rider's meeting, get signed in, and set up out on track (with little access to food, water, or bathroom), spend the next 8+ hours shooting in pouring rain or oppressive heat, then spend the next two days in front of a computer looking at and editing thousands of images and uploading them to your website, and then have maybe a half dozen people buy a download or print from you? And then look back at the past three days, and the sales, and realize how much money you actually lost?
Here's my 2 cents. If you want to shoot motorsports, do it because you love being at the track, because you love the sounds, the smells, the people. Work on building skills and making connections. Then, maybe after a few years, you can start getting some pocket money (you aren't really losing money because you would be at the track anyway, for the love of being at the track). And then, maybe if you are lucky, some publication decides they want to pay you for your pictures. If that's your attitude going in then it all becomes a bonus. But if you go into it thinking you're gonna be a "big time" motorsports photographer for a racing publication, you are going to get severely let down real quick.