I don't dispute the existence of poor customer service in the motor trade. On the contrary, its everywhere. Good customer service is the exception, not the rule. But that said, you're buying a car and it's just a transaction. A salesman has never enhanced the process for me - they are an obstacle between me and the car I want at the price I want to pay. I'm certainly not going to base any of my car choices based on the initial interaction with the sales staff. Who cares? They won't after they've sold it to you anyway!
Unless you're factory ordering a new car (In which case you're probably going to use a broker/carwow/whatever anyway) then your choice of dealer especially when looking at most specialist cars will be dictated not by who rushed over with a biscuit and a cup of tea fastest but who actually has the spec you want in stock anyway. So these stories of walking out purely on the basis of the sales staff ignoring you and buying somewhere else? Unless these people wanted a Generic Crossover 1.6 with Black Wheels and lived within 10 miles of 3 different insert-mainstream-manufacturer-here dealers how often do they happen really?
The internet is full of these stories - usually the same theme, walked into a dealer, expected a red carpet, didn't get it, ran out to another dealer instead. Bonus points for anecdotes where the poster or someone they knew was wearing old jeans and a hoody and later paid cash for a Ferrari.
I've been ignored in showrooms - I've simply asked again for assistance until such time as I received it. I'm not looking for a new friend, I just want to buy or look at a car. Generally I telephone in advance anyway - I'd imagine that part of the problem is that most salesmen quickly learn the conversion rate from walk-in to sale is very low, especially when you get the usual test pilots who need a good drive of the auto and the manual version of the entire Evo Car of the Year shortlist to make their decision -then buy something else anyway. Very few people buying expensive cars will do so after randomly showing up unannounced expecting to be given free and unlimited access to the demonstrator fleet and the attitude you're getting from dealers reflects this reality I'd suggest.
Much of this comes from the salesman/commission business model where a salesman is judged and earns purely on the basis of what they sell with no real eye for future brand loyalty. Were they salaried with no bonus for selling car you'd probably get a different experience as the incentive to profile is gone, but we're not there and you have to work with what you have, don't you?
I'd question the value of test drives in the car buying process anyway. For me, I find they are often counter productive. You never get enough time to really get to know a car and are instead left with often false initial impressions. I've bought the wrong car off the back of test drives and I've also seen the 'wow this car is great' feeling gradually move to 'If I never drive this car again I won't care' over the period of, say, a weeks rental. These things take time, a test drive only ever offers a taste.