High nitrates in the water will promote algae more than plants (10ppm nitrate is fine for vascular plants).
If it were nitrate alone in the water, you might justify not changing much. But how about colorants (water yellows with time and pollution), all the myriad DOC (dissolved organic compounds/dissloved organic carbons - pheromones, hormones, phenols, aldehydes, etc.), loss of KH due to normal nitrification leading to downward drift in pH, increase in TDS (total dissolved solids) due to evapotation and feeding ...et cetera ad infinitum.
IMHO, not changing water is just about the worst thing you can do to a tank.
Water is cheap, change it often.