The only difference is now that merchant has 0.25 BTC instead of $50. Maybe the merchant immediately sells for dollars, but in some cases they hold a percentage. This means that Option 2 slowly increases bitcoin ownership. This is velocity.
More to the point, you bought 0.25 BTC, bidding up the price. If the merchant
immediately sells the BTC, it's a wash as far as bidding the price of BTC up or down (but the merchant sees greater value in BTC, incentivizing them toward holding in the future). If the merchant doesn't immediately sell, for the duration that they do hold - whether just a day or a month or long term - there are fewer bitcoins available on the market, pushing the price up.
So a purchase made through buy-and-replace is at worst slightly positive for the BTC price, and at best substantially positive.
Simpler way to think about it: The more bitcoins "in the pipeline" of transaction processing, the less available on the market, hence the higher the price. Like if you had a bunch of buckets of water with hoses running between them. The more hoses and the more full they are, the less water will be in the buckets at any given time. Less water available means water is scarcer, dearer, more expensive.
What about people just spending their coins? Insofar as
this is understood (consciously or unconsciously), any spending that happens will merely be in lieu of selling, by holders who are looking to unload some in order to rebalance their Bitcoin-to-fiat portfolio. In that case the same applies: at worst slightly positive, at best substantially positive.
But what about the case of an impulse buy where a holder acts temporarily against their own portfolio balancing target and spends their coins even though they are already low on BTC? Well there is no obvious reason to think there wouldn't be an equal number of holders who temporarily act against their portfolio target in the opposite direction. It's a wash.
Overall, then, merchant adoption is at worst slightly positive for the price, just in terms of the economics, not even taking into account the positive publicity effects and the increased value in the eyes of merchants who are now getting a revenue stream via Bitcoin.
All that said, I don't think merchant adoption is the main thing that will drive the price higher for the next few years. The main thing is good old fashioned hoarding.
Conclusion:
Don't worry about merchant adoption. If it happens, good, it will just add a little extra boost to the exponential growth. If it doesn't it's nothing to worry about. Investors are the ones that will drive the lion's share of growth for the foreseeable future.