Glad you ask these questions, Psion!
Psion said:
I want to put some [chases] in my game. Especially considering I am just about to usher my players into the world of airships.
So, a few questions to put forth.
1) I have Grim Tales. Do I need
Hot Pursuit. (Yes, Barsoomcore and Gareth can feel free to tell my why I do, but I'd like to hear some other perspectives.

)
Yes, absolutely get
Hot Pursuit. The way it provides for different manuevers and is flexible to a player's wildest dreams are its high marks. And its low marks are, well, it's another system to learn (though it's pretty simple).
Psion said:
what are some scenarios that would make the players hesitant to stand and fight, given it is almost a given in D&D. I am thinking race situations and luring the enemy are two possibilities. Any others?
I posted about reasons why a high-level character would hold back, and I think these are really just universal strategy points that players may (or may not) consider:
Quickleaf said:
1. A sporting chance: Bravado is a common trait of heroic figures. The idea that a master of some art loves to be tested may lead to PCs choosing not to try other options just for the joy of testing themselves (and proving their superiority!). Perhaps the PC simply doesn’t believe that anyone could pull a fast one on them. In either case, of such role-playing is appropriate to the character’s personality, it merits extra experience points, anywhere from 10 to 20 times the character’s level.
2. Conservation of energy: You never know when you’re going to need those vastly powerful yet limited resources, so it is better to keep them stored up for truly desperate situations. Sometimes it makes sense not to waste time and energy on the little fish when there’s a much greater threat on the horizon.
3. I’ve got a reputation to maintain: In the case of reputable heroes, sending the entire party against a meager thief and interrogating him with force and magic would be detestable to anyone observing. Such a disproportionate response is never seen as heroic unless their enemy is truly hated and feared by the public. When others witness or learn of the PC’s dishonorable actions, their reputations could suffer.
4. Observed by their enemies: In this case, a PC might not want to give away her hand too son to her enemies. Once an enemy knows a PC’s strengths, they can tailor defenses to counteract those strength. Embroiled in political intrigue, the PCs often won’t know when their enemy’s servants are observing them.
5. He’s worth more alive: If an enemy can be questioned for useful information, or traded for ransom or a favor later, it’s better to keep them alive than, say, cast disintegrate.
6. Deterrence: The PCs and their enemies may have vast resources that could destroy cities if not nations. If neither side is willing to risk the massive loss of life that would follow an all-out conflict, they may resort to more under-handed methods. Often this involves researching and spying on your enemy to find their weak spot, and exploiting it.
Psion said:
Second, another scenario is that where the PCs are superior, but the bad guy has something and is trying to get away. The problem is that (especially at the level my group is at) groups often have access to capabilities that can end chases fairly quickly. Teleport and the like.
This is tricky to do without making the players feel you're pulling the "I'm the GM, screw you" card, and, as you point out, it is compounded by access to D&D spells. I remember a great desert chase I had planned; round 1 the mage casts
hold person and drops the target out of their saddle. Chase is over before it began.
To really address this, we need to look at a few assumptions about magic & crime:
1. How is the casting of spells viewed in civilized parts of the world? Is it even legal? Must you file a request to be legally allowed to cast a spell in a city? What are the consequences for breaking this law?
2. In a world where a police officer can cast
hold person on a fleeing criminal, what chance does crime have? The criminals surely have grown smarter and developed their own magical counter-abilities. What about casting
mirror image prior to a chase, with the addition that several of the villains cronnies (dressed in identical clothes) join the chase. So now you're not chasing one, but 3, 4, 5, or more bad guys, some of which aren't even real! And it's even more complex if the villains throw in a decoy object. "Ok, I surrender! Just don't hurt me! Take this magical gizmo!"
3. If the players can take off their kit gloves and break the law, then surely criminals will respond likewise. They will employ all manner of tactics that they never could in a city, such as: Smearing contact poison on the object (or its decoy). Summoning the city watch to stop the people accosting them. Ducking into a crowd and performing a swift disguise (might need a feat to do that!). If the party has teleportation, give the criminal teleportation. If the party has hold person, have the criminal cast it upon them first. Fleeing villain might go through an escape route with magically enchanted mirrors, or some other trap. Taking a hostage. Throwing a magical deterrent behind them (a golem-like creature that drains spellcasting levels or shoots poison darts). Drops some caltrops...poisoned or enchanted of course. Flee into a really, really dangerous area (foundry with sparks everywhere, an asteroid belt, a sleeping dragon's lair where any speaking wakes the dragon, an anti-magic field).
As an aside, why are the PCs facing inferior opponents anyhow?
