Who are the 'minnows' in test cricket currently? Certainly there's not more than 1. Bangladesh is one, and I don't think India, South Africa, England, Australia and Sri Lanka should play too many test series against them at present.
Once
1. Bangladesh is very competitive against first-choice Pakistan, Newzealand, West Indies teams,
AND/OR
2. some of the top 5 teams start having a horrrid time against Pakistan, Newzealand, West Indies
...they should start playing regularly against those teams.
Till then,
1. Top 5 teams should play regulary among themselves and with the next 3 teams in the (imaginary) 2nd tier.
2. Bangladesh should have regular series with those 3 teams in the (imaginary) 2nd tier.
This will result in both
1. Viewers not being tortured with too many absolutely boring whitewashes.
2. A chance to the Bangladesh team to improve its standards by playing with Pakistan, NZ, WI.
If that results in less number of batsmen averaging over 50, I'm very happy with it.