Accurate keywords are everything to minisites, *unless* you plan to do a lot of extra work like linkbuilding, article submissions, and some heavy SEO. If you want to do all that, then altered/brandable names might work as minisites, depending on how good a job you do.
If your plan is to just build a minisite and then leave it, keyword accuracy is paramount if you actually want it to succeed. Here's why:
Unless your dn has great type-in traffic naturally, the only way you'll get traffic to it, without a lot of SEO and marketing etc., is to get it on the first page of Google and other engines. That way people who are searching for your term will see your site right away and hopefully check it out since it is the primary domain/site with the term/phrase they just searched.
When people search 'garden tools', your minisite named gardenToolz.com will not even be close to page 1 on their search results, google will not index typos and throw them into the mix, high up, with properly-spelled names. Your site may be on page 1 when they search 'garden toolz'... but almost no one in the world searches that term. You might get 10 visits a month, so it really doesn't matter if you're on page 1 when people search 'garden toolz', because almost no one does (I'm making assumptions here - haven't actually looked into the stats of gardentoolz
).
You want to pick a niche name to use as a minisite, and you want the spelling to be correct, and you want that niche name to have enough monthly searches to be worth your while if/when your site eventually lands on page 1 of google. Niches work perfectly; if it's too broad/generic/popular of a name, chances are you'll have a ton of competition, by large sites with a lot of money to spend on keeping their site on page 1 of the engines, and your little humble minisite won't get anywhere close to page 1, or even page 10. But if you choose a NICHE name for the minisite, chances are there'll be almost no competition and your site will eventually hit page 1, spot 1 on the engines.
Once again, number of monthly searches for the exact term is important; if your site is on page 1 of google, but the term is only searched for 10 times a month, you're going to make zilch income. If your term is searched for 1000 or 5000 times per month, you have a very good chance of income, and good income if there is a generous advertiser competition for your term, in adsense links.
To sum: 99 names out of a hundred should be EXACT SPELLING when being intended for minisites. Find terms with advertiser competition, and healthy monthly searches. Use only dot.com for niches, unless it's a great niche with extremely healthy searches, but with little competition for page 1 on google (for example, if other extensions are taken but all of them are parked pages, not developed); in that case, you might experiment with the dot.net/info/org/us or whatever, if you really want to.
There are still a lot of great dot.com's out there to be discovered and made into minisites. I still daily find hundreds of dot.com's with between 500 and 5000 monthly searches, and some with more than that. Usually I only choose very clear names. I never use brandables or miss-spelled names for minisites anymore. Tried a lot of those in the beginning, and not one of them paid off. I've let about 30 of those drop, and will drop a few more soon. Correct spelling only, and only keywords/phrases that actually get good searches.
Even if I have to get a little inventive: this name had decent stats, so I decided to nab it and switch it up a little:
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