  Using the Andrade-derived Sundberg-Cooper rheology, we apply several
improvements to the secular tidal evolution of TRAPPIST-1e and the early
history of Pluto-Charon under the simplifying assumption of homogeneous bodies.
By including higher-order eccentricity terms (up to and including $e^{20}$), we
find divergences from the traditionally used $e^{2}$ truncation starting around
$e=0.1$. Order-of-magnitude differences begin to occur for $e>0.6$. Critically,
higher-order eccentricity terms activate additional spin-orbit resonances.
Worlds experiencing non-synchronous rotation can fall into and out of these
resonances, altering their long-term evolution. Non-zero obliquity generally
does not generate significantly higher heating; however, it can considerably
alter orbital and rotational evolution. Much like eccentricity, obliquity can
activate new tidal modes and resonances. Tracking the dual-body dissipation
within Pluto and Charon leads to faster evolution and dramatically different
orbital outcomes. Based on our findings, we recommend future tidal studies on
worlds with $e\geq0.3$ to take into account additional eccentricity terms
beyond $e^{2}$. This threshold should be lowered to $e>0.1$ if non-synchronous
rotation or non-zero obliquity is under consideration. Due to the poor
convergence of the eccentricity functions, studies on worlds that may
experience very high eccentricity ($e\geq0.6$) should include terms with high
powers of eccentricity. We provide these equations up to $e^{10}$ for arbitrary
obliquity and non-synchronous rotation. Finally, the assumption that
short-period, solid-body exoplanets with $e\gtrsim0.1$ are tidally locked in
their 1:1 spin-orbit resonance should be reconsidered. Higher-order spin-orbit
resonances can exist even at these relatively modest eccentricities, while
previous studies have found such resonances can significantly alter
stellar-driven climate.
