Without adequate market studies of your specific neighborhood, you may over-improve the dwelling. I think that before sinking cash into a unit to upgrade it (vs. using the cash to acquire additional units), your rental comps have to be solid, taking into account the actual vacancy losses incurred by higher-cost units.
As @Rob Gribben pointed out, you might get more money, and even a better tenant, but will you have more turnover and is the cash worth the downtime? Canton is a funny market, and I don't think you have too many folks renting for more than 2-3 years because it's a young crowd there for their first job before they get married/sick of the bar scene/enough money to buy a place. I'd personally be weary of improving beyond the B range of rentals in that neighborhood.
In Oahu, your place has to radically overpriced or a total dump not to rent within a weekend. When we were looking for places, our application was usually in a stack of 4-5 fully qualified, great tenants, and 10 more "ok" tenants.