I think that's a given. Given your take on assets and appreciation and lack of knowledge on what a speculative market is...
Watches, particularly Rolex are a traditional asset bubble. Look at every asset bubble that has ever existed, they eventually pop. It might take 10 years, it might take 20. Maybe even 50, who knows. But 'No King rules forever' and that includes Rolex. Rolex are only popular now, will it stay that way who knows? Arguably it will, Rolex have the same brand strength as Coca Cola, it's that synonymous. But nothing in life is guaranteed except death and taxes. (look at previous booms / busts - Dotcom for example)
Rolex right now are a fantastic speculative investment for quick returns. Long-term its questionable, but short-term they're one of the most liquid tangible assets you could possibly own (right now). But as with all investments, and all investment companies have a compulsory regulatory statement that says something along the lines of 'history is not an accurate predictor of the future, your returns may vary'. There's a reason we put this disclosure up. History isn't a good predicator. You can look at the CAPM (Capital Asset Pricing Model) and that will show you what using history as predictor gets you. Fama and French (if I remember their names correctly, been a while since I studied financial theory) they improved upon it, but even with their adjustments. History is borderline useless. A fantastic example of this is a recent company called NMC Health... (Dubai based Healthcare trust) - They lied, for ~3 years on their financial statements, claiming they were in profit. Thus institutional investors used this information and viewed the company as undervalued, and thus invested millions upon millions into this company. Well if you check their recent history... you'll find they're no longer active on a stock market. Their fraud was found out and yeah... everyone invested has lost money. Fun times.
Lastly, you also don't understand the concept of time to money value, ie inflation. If you buy a watch today at £10,000, and sell it next year for £11,000. You have not made £1,000. You have made less than a £1,000 because of inflation. As for a measure for inflation, well that depends if you judge by RPI/CPI or if you look at the price of goods. Even conservative estimates of real world inflation are around 3%-5%. All is not as it seems with money... it isn't black and white, and that's why we have the financial markets and financial institutions. So you can't base your calculations on the assumption that money will always have the same buying power.
Furthermore this ignores monetary and fiscal policy, ie the supply of money and the value of money. For example, your national bank, Bank of England, has a set target for inflation of around 2%. They achieve this by modifying the interest rate. Interest is effectively the cost of borrowing, or more how expensive money is.
When interest rates are low, inflation becomes higher as the cost of borrowing money is cheaper and thus buying power reduces (as more people borrow money). It's the reason the UK Housing market is so insane right now, prices are massively inflated because the cost of borrowing money is very low. Right now we're in incredible low interest times thus you would expect inflation to raise. Plus, with Quantitive Easing measures we're likely to see money devalue very quickly. So all is not how/what it seems. Comparing buying power for example... Oil Prices... Grain Prices... Precious Metals, these are good indicators to use to find the true value of money.
This is why you cannot compare money across time, easily at least.
Anyway
TLDR, top tip. Don't pay more than 20% above retail for anything that is an asset bubble. Even if you end up losing certain returns, your capital should be protected. And find a more accurate way of measuring moneys future value. (NPV)